Balance charging circuit for series-connected storage cells and balance charging method for series-connected storage cells

ABSTRACT

A coil is electrically connected to one of storage cells to charge it, and after that, the coil is electrically connected to the other one thereof to charge it. In a first charging period, a path of a charging current flowing into a reference voltage through the coil is formed, in a second charging period, a path of a charging current flowing into a second cell from the coil is formed, in a third charging period, a path of a charging current flowing into the reference voltage through the coil is formed, and in a forth charging period, one end of the coil is electrically conducted with one end of the first cell and another end of the coil is electrically conducted with another end of the first cell to form a path of a charging current flowing into the first cell from the coil.

TECHNICAL FIELD

The present invention relates to a balance charging circuit forseries-connected storage cells and a balance charging method forseries-connected storage cells.

BACKGROUND ART

Storage cells (hereinafter referred to as cells) such as secondarybatteries and capacitors are often used to be connected in series. Whenthe cells are connected in series, voltages at both ends of theseries-connected cells increase. In view of this, when theseries-connected cells are assumed as a single module, that is, a singlepackage, a voltage booster type of charging circuit using an inductor orthe like is necessary to charge the series-connected cells by alow-voltage power supply. A charging circuit 503 in FIG. 109 is aconventionally known charging circuit for series-connected cells.

The charging circuit 503 includes a coil (an inductor) L1, a switch S1,a switch S2, and a charging control circuit Control 5, and one end ofthe coil L1 is connected to an input terminal 501, one end of the switchS1 is connected to an output terminal 502, and one end of the switch S2is connected to a reference voltage terminal. Another end of the coil L1is connected to the other end of the switch S1 and the other end of theswitch S2. Further, the charging control circuit Control 5 controls onand off of the switch S1 and the switch S2. Further, series-connectedcells are connected to the one end of the switch S1.

The switch S2 is turned on by the charging control circuit Control 5.Next, an input voltage Vin is input from the input terminal 501, and acharging current to charge the series-connected cells with electriccharge is stored in the coil L1.

Then, the switch S2 is turned off and the switch S1 is turned on by thecharging control circuit Control 5. After that, the series-connectedcells are charged with electric charge by the charging current chargedin the coil L1.

The series-connected cells can be charged in this manner.

In the meantime, capacitance values of storage cells differ from eachother due to their production processes.

In such a case, if there is a variation in capacitance value betweenseries-connected cells, a variation in voltage occurs between theseries-connected cells after charging is performed. When the variationin voltage occurs, a voltage concentrates on one of the series-connectedcells, which causes such a problem that its life is shortened. In orderto solve this problem, there has been known a voltage balance correctioncircuit (a cell balancing circuit) for series-connected cells forequalizing voltages of respective cells in the series-connected cells tomaintain voltage balance (see, for example, Patent Document 1).

A cell balancing circuit 504 in FIG. 109 is a conventional cellbalancing circuit described in Patent Document 1.

The cell balancing circuit 504 includes a coil L2, a switch S3, a switchS4, a cell Cell1, a cell Cell2, and a cell-balancing control circuitControl 6. The cell Cell1 and the cell Cell2 are connected in series andhave one series-connected end connected to the output terminal 502 andanother series-connected end connected to a reference voltage terminal.Further, one end of the coil L2 is connected to a contact point betweenthe cell Cell1 and the cell Cell2, one end of the switch S3 is connectedto the output terminal 502, one end of the switch S4 is connected to thereference voltage terminal, and the other end of the coil L2 isconnected to the other end of the switch S3 and the other end of theswitch S4. Further, the cell-balancing charging circuit Control 6controls on and off of the switch S3 and the switch S4.

The switch S4 is turned on by the cell-balancing control circuit Control6. Among electric charge charged in the cell Cell2, a current tomaintain voltage balance between the series-connected cells is flowedinto the coil L2 so as to store a charging current.

Then, the switch S4 is turned off and the switch S3 is turned on by thecell-balancing control circuit Control 6. After that, the cell Cell1 ischarged with electric charge by the charging current charged in the coilL2 so as to maintain the voltage balance between the series-connectedcells.

As mentioned earlier, each of the charging circuit and the cellbalancing circuit needs one coil.

If the charging circuit is combined with the cell balancing circuit, abalance charging circuit for series-connected cells which charges theseries-connected cells and maintains voltage balance between therespective cells is attained.

FIG. 109 is entirely a view illustrating a conventional balance chargingcircuit for series-connected cells. The conventional balance chargingcircuit for series-connected cells is constituted by the chargingcircuit 503 for charging the series-connected cells and the cellbalancing circuit 504 for maintaining voltage balance between therespective cells.

The charging circuit 503 includes a coil (an inductor) L1, a switch S1,a switch S2, and a charging control circuit Control 5, and one end ofthe coil L1 is connected to an input terminal 501, one end of the switchS1 is connected to an output terminal 502, and one end of the switch S2is connected to a reference voltage terminal. Another end of the coil L1is connected to the other end of the switch S1 and the other end of theswitch S2. Further, the charging control circuit Control 5 controls onand off of the switch S1 and the switch S2.

The cell balancing circuit 504 includes a coil L2, a switch S3, a switchS4, a cell Cell1, a cell Cell2, and a cell-balancing control circuitControl 6, and the cell Cell1 and the cell Cell2 are connected in seriesand have one series-connected end connected to the output terminal 502and another series-connected end connected to the reference voltageterminal. Further, one end of the coil L2 is connected to a contactpoint between the cell Cell1 and the cell Cell2, one end of the switchS3 is connected to the output terminal 502, one end of the switch S4 isconnected to the reference voltage terminal, and the other end of thecoil L2 is connected to the other end of the switch S3 and the other endof the switch S4. Further, the cell-balancing charging circuit Control 6controls on and off of the switch S3 and the switch S4.

FIGS. 110 to 113 are views to explain operations of the conventionalbalance charging circuit for series-connected cells.

Firstly, the switch S2 is turned on by the charging control circuitControl 5. Next, an input voltage Vin is input from the input terminal501, and a charging current to charge the series-connected cells withelectric charge is stored in the coil L1. A path of the charging currentis indicated by a dotted arrow in FIG. 110.

Then, the switch S2 is turned off and the switch S1 is turned on by thecharging-amount control circuit Control 5. After that, theseries-connected cells are charged with the charging current charged inthe coil L1. A path of the charging current is indicated by a dottedarrow of FIG. 111.

In parallel with the afore-mentioned operation of the charging controlcircuit Control 5, the switch S4 is turned on by the cell-balancingcontrol circuit Control 6. Among the electric charge charged in the cellCell2, a current to maintain voltage balance between theseries-connected cells is flowed into the coil L2 so as to store acharging current. A path of the charging current is indicated by adotted arrow of FIG. 112.

Then, the switch S4 is turned off and the switch S3 is turned on by thecell-balancing control circuit Control 6. After that, the cell Cell1 ischarged with the charging current charged in the coil L2 so as tomaintain the voltage balance between the series-connected cells. A pathof the charging current is indicated by a dotted arrow of FIG. 113.

In the conventional balance charging circuit for series-connected cells,the series-connected cells are charged with electric charge and thevoltage balance between the series-connected cells is maintained assuch, so as to obtain an output voltage Vout from the output terminal502.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: JP 2008-17605 A

SUMMARY OF THE INVENTION Problem to be Solved

However, the conventional balance charging circuit for series-connectedcells described in Patent Document 1 has the following problem. In theconventional balance charging circuit for series-connected cells, twocoils in total, i.e., a coil for charging the series-connected cellswith electric charge and a coil for maintaining voltage balance betweenthe series-connected cells are necessary. That is, a coil is larger insize than components such as a switch, and therefore, using many coilscauses such a problem that a circuit is upsized as a whole.

Further, in order to maintain voltage balance between theseries-connected cells by use of the conventional balance chargingcircuit for series-connected cells, another charging circuit isnecessary separately, as has been explained with reference to FIG. 109.That is, by performing two operational stages, i.e., by performingcharging by this charging circuit (see FIG. 110 and FIG. 111), and then,maintaining voltage balance between the series-connected cells by theoperation of the balancing circuit (see FIG. 112 and FIG. 113), chargingvoltage balance between the series-connected cells is maintained. Asdescribed, it is necessary to provide a charging circuit in addition tothe balance charging circuit, which causes such a problem that a circuitis upsized as a whole.

The present invention has been made in view of the above-mentionedcircumstances, and an object of the present invention is to provide abalance charging circuit for series-connected storage cells and abalance charging method for series-connected storage cells each of whichcan combine a coil for charging series-connected cells with electriccharge and a coil for maintaining voltage balance between theseries-connected cells, that is, can realize these coils by a singlecoil and which attains a smaller circuit configuration as a whole.

Solution to the Problem

A balance charging circuit for series-connected cells according to oneembodiment of the present invention is a balance charging circuit forcharging, in a balanced manner, a first storage cell and a secondstorage cell connected in series and having one series-connected endconnected to an output terminal and another series-connected endconnected to a reference voltage, and the balancing charging circuitincludes: a coil provided in common for the first storage cell and thesecond storage cell and temporarily storing a power supplied from apower supply to charge the first storage cell and the second storagecell; and a switch section for electrically connecting the coil to oneof the first storage cell and the second storage cell to charge the oneof the first storage cell and the second storage cell and then forelectrically connecting the coil to the other one of the first storagecell and the second storage cell to charge the other one of the firststorage cell and the second storage cell. By employing thisconfiguration, it is not necessary to provide a plurality of coils andit is possible to downsize a whole configuration of the balance chargingcircuit more.

In the balance charging circuit for series-connected storage cells, itis preferable that: the switch section includes a plurality of switchesfor switching a path of a charging current flowing in the coil; thebalance charging circuit further includes a control circuit forcontrolling the plurality of switches to be turned on and off and forsetting repeatedly in turn a first charging period in which the coil ischarged with a charging current to charge the second cell, a secondcharging period in which the second cell is charged with the chargingcurrent thus charged in the coil, a third charging period in which thecoil is charged with a charging current to charge the first cell, and afourth charging period in which the first cell is charged with thecharging current thus charged in the coil; and in the first chargingperiod, the control circuit controls the plurality of switches to beturned on and off to form a path of a charging current flowing into thereference voltage terminal through the coil, in the second chargingperiod, the control circuit controls the plurality of switches to beturned on and off to form a path of a charging current flowing into thesecond storage cell from the coil, in the third charging period, thecontrol circuit controls the plurality of switches to be turned on andoff to form a path of a charging current flowing into the referencevoltage through the coil, and in the fourth charging period, the controlcircuit controls the plurality of switches to be turned on and off toelectrically conduct one end of the coil to one end of the first cell,electrically conduct another end of the coil to another end of the firstcell, and form a path of a charging current flowing into the first cellfrom the coil. By employing this configuration, it is not necessary toprovide a plurality of coils and it is possible to downsize a wholeconfiguration of the balance charging circuit more.

The plurality of switches may include a first switch having one endconnected to a contact point where the first cell and the second cellare connected to each other, a second switch having one end connected toan input terminal, a third switch having one end connected to thereference voltage, a fourth switch having one end connected to theoutput terminal, a fifth switch having one end connected to thereference voltage, and a sixth switch having one end connected to thecontact point where the first cell and the second cell are connected toeach other; one end of the coil may be connected to another end of thefirst switch, another end of the second switch, and another end of thethird switch, and another end of the coil may be connected to anotherend of the fourth switch, another end of the fifth switch, and anotherend of the sixth switch; and in the first charging period, the controlcircuit may turn on the second and sixth switches and turn off thefirst, third, fourth, and fifth switches, in the second charging period,the control circuit may turn on the third and sixth switches and turnoff the first, second, fourth, and fifth switches, in the third chargingperiod, the control circuit may turn on the second and fifth switchesand turn off the first, third, fourth, and sixth switches, and in thefourth charging period, the control circuit may turn on the first andfourth switches and turn off the second, third, fifth, and sixthswitches. By employing this configuration, it is not necessary toprovide a plurality of coils and it is possible to downsize a wholeconfiguration of the balance charging circuit more.

Further, the plurality of switches may include a first switch having oneend connected to a contact point where the first cell and the secondcell are connected to each other, a second switch having one endconnected to an input terminal, a third switch having one end connectedto the reference voltage, a fourth switch having one end connected tothe output terminal, a fifth switch having one end connected to thereference voltage, and a sixth switch having one end connected to thecontact point where the first cell and the second cell are connected toeach other; one end of the coil may be connected to another end of thefirst switch, another end of the second switch, and another end of thethird switch, and another end of the coil may be connected to anotherend of the fourth switch, another end of the fifth switch, and anotherend of the sixth switch; and in the first charging period, the controlcircuit may turn on the second and fifth switches and turn off thefirst, third, fourth, and sixth switches, in the second charging period,the control circuit may turn on the third and sixth switches and turnoff the first, second, fourth, and fifth switches, in the third chargingperiod, the control circuit may turn on the second and fifth switchesand turn off the first, third, fourth, and sixth switches, and in thefourth charging period, the control circuit may turn on the first andfourth switches and turn off the second, third, fifth, and sixthswitches. By employing this configuration, it is not necessary toprovide a plurality of coils and it is possible to downsize a wholeconfiguration of the balance charging circuit more.

The plurality of switches may include a first switch having one endconnected to the output terminal, a second switch having one endconnected to an input terminal, a third switch having one end connectedto the reference voltage, a fourth switch having one end connected tothe input terminal, and a fifth switch having one end connected to acontact point where the first cell and the second cell are connected toeach other; one end of the coil may be connected to another end of thefirst switch, another end of the second switch, and another end of thethird switch, and another end of the coil mat be connected to anotherend of the fourth switch and another end of the fifth switch; and in thefirst charging period, the control circuit may turn on the second andfifth switches and turn off the first, third, and fourth switches, inthe second charging period, the control circuit may turn on the thirdand fifth switches and turn off the first, second, and fourth switches,in the third charging period, the control circuit may turn on the thirdand fourth switches and turn off the first, second, and fifth switches,and in the fourth charging period, the control circuit may turn on thefirst and fifth switches and turn off the second, third, and fourthswitches. By employing this configuration, it is not necessary toprovide a plurality of coils and it is possible to reduce the number ofswitches, thereby making it possible to downsize a whole configurationof the balance charging circuit more.

The plurality of switches may include a first switch having one endconnected to the output terminal, a second switch having one endconnected to an input terminal, and a third switch having one endconnected to the reference voltage; one end of the coil may be connectedto another end of the first switch, another end of the second switch,and another end of the third switch, and another end of the coil may beconnected to a contact point where the first cell and the second cellare connected to each other; and in the first charging period, thecontrol circuit may turn on the second switch and turn off the first andthird switches, in the second charging period, the control circuit mayturn on the third switch and turn off the first and second switches, inthe third charging period, the control circuit may turn on the thirdswitch and turn off the first and second switches, and in the fourthcharging period, the control circuit may turn on the first switch andturn off the second and third switches. By employing this configuration,it is not necessary to provide a plurality of coils and it is possibleto reduce the number of switches, thereby making it possible to downsizea whole configuration of the balance charging circuit more.

The plurality of switches may include a first switch having one endconnected to the output terminal, a second switch having one endconnected to an input terminal, and a third switch having one endconnected to the reference voltage; the balance charging circuit mayfurther include a capacitor having one end connected to the referencevoltage, and a diode having a cathode connected to a contact point wherethe first cell and the second cell are connected to each other; one endof the coil may be connected to another end of the first switch, anotherend of the second switch, and another end of the third switch, andanother end of the coil may be connected to another end of the capacitorand an anode of the diode; and in the first charging period, the controlcircuit may turn on the second switch and turn off the first and thirdswitches, in the second charging period, the control circuit may turn onthe third switch and turn off the first and second switches, in thethird charging period, the control circuit may turn on the third switchand turn off the first and second switches, and in the fourth chargingperiod, the control circuit may turn on the first switch and turn offthe second and third switches. By employing this configuration, it isnot necessary to provide a plurality of coils and it is possible tofurther reduce the number of switches, thereby making it possible todownsize a whole configuration of the balance charging circuit more.

It is preferable that the control circuit sets times for turning on theswitches in the second and fourth charging periods so that the chargingcurrent of the coil becomes zero at the end of the second and fourthcharging periods. By employing this configuration, a time for removing aresidual current of the coil at the end of the second and fourthcharging periods can be eliminated at the beginning of the first andthird charging periods. It is also possible to prevent power attenuationwhich occurs when a refresh current to a power supply side flows into aparasitic resistor of each element in a current path in the first andthird charging periods.

A balance charging circuit for series-connected storage cells accordingto another embodiment of the present invention is a balance chargingcircuit for charging, in a balanced manner, first to Nth (N is aninteger of 2 or more, the same applies hereinafter) storage cellsconnected in series and having one series-connected end connected to anoutput terminal and another series-connected end connected to areference voltage terminal, and the balancing charging circuit includes:

a coil provided in common for the first to Nth storage cells andtemporarily storing a power supplied from a power supply connected tothe input terminal to charge the first to Nth storage cells; and

a plurality of first switches for electrically connecting the coilbetween the input terminal and the reference voltage; and

a plurality of second switches for electrically connecting both ends ofthe coil to both ends of each of the first to Nth storage cells tocharge the each of the first to Nth storage cells. By employing thisconfiguration, it is not necessary to provide a plurality of coils andit is possible to downsize a whole configuration of the balance chargingcircuit more.

It is preferable that: the balance charging circuit for series-connectedstorage cells further includes a control circuit for repeatedly setting,in a random manner, each of the first to Nth charging periods wherein akth (1≦k≦N) coil charging period in which the plurality of firstswitches are controlled to be turned on and off to charge the coil witha charging current to charge the kth storage cell, and a kth storagecell charging period in which the plurality of second switches arecontrolled to be turned on and off to charge the kth storage cell withthe charging current charged in the coil in the kth coil charging periodare taken as a kth charging period for charging the kth storage cell;and

in the kth coil charging period, the control circuit controls theplurality of first switches to be turned on and off to form a path of acharging current flowing into the reference voltage terminal from theinput terminal through the coil, and

in the kth storage cell charging period, the control circuit controlsthe plurality of second switches to be turned on and off to form a pathof a charging current flowing into the kth storage cell from the coil.By employing this configuration, it is not necessary to provide aplurality of coils and it is possible to downsize a whole configurationof the balance charging circuit more.

It is preferable that: the plurality of first switches include a firstcoil connection switch having one end connected to the input terminaland another end connected to one end of the coil, and a second coilconnection switch having one end connected to another end of the coiland another end connected to the reference voltage terminal; and theplurality of second switches include first to Nth storage cell lowerside connection switches each having one end connected to a lower sideof each of the first to Nth storage cells and another end connected tothe one end of the coil, and first to (N−1)th storage cell upper sideconnection switches each having one end connected to an upper side ofeach of the first to (N−1)th storage cells and another end connected tothe one end of the coil. By employing this configuration, it is notnecessary to provide a plurality of coils and it is possible to downsizea whole configuration of the balance charging circuit more.

In the kth coil charging period, the control circuit may turn on thefirst and second coil connection switches, and turn off the first to Nthstorage cell lower side connection switches and the first to (N−1)thstorage cell upper side connection switches; and in the kth storage cellcharging period, the control circuit may turn off the first and secondcoil connection switches, turn on the kth storage cell lower sideconnection switch and the kth storage cell upper side connection switch,and turn off the switches other than the kth storage cell lower sideconnection switch among the second to Nth storage cell lower sideconnection switches, and the switches other than the kth storage cellupper side connection switch among the first to (N−1)th storage cellupper side connection switches. By employing this configuration, it isnot necessary to provide a plurality of coils and it is possible todownsize a whole configuration of the balance charging circuit more.

In the first coil charging period, the control circuit may turn on thefirst and second coil connection switches and the first storage cellupper side connection switch, and turn off the first to Nth storage celllower side connection switches and the third to (N−1)th storage cellupper side connection switches; in the Mth (2≦M≦N) coil charging period,the control circuit may turn on the first and second coil connectionswitches, and turn off the first to Nth storage cell lower sideconnection switches and the third to (N−1)th storage cell upper sideconnection switches; in the Mth storage cell charging period, thecontrol circuit may turn off the first and second coil connectionswitches, turn on the Mth storage cell lower side connection switch andthe Mth storage cell upper side connection switch, and turn off theswitches other than the Mth storage cell lower side connection switchamong the first to Nth storage cell lower side connection switches, andthe switches other than the Mth storage cell upper side connectionswitch among the first to (N−1)th storage cell upper side connectionswitches. By employing this configuration, it is not necessary toprovide a plurality of coils and it is possible to downsize a wholeconfiguration of the balance charging circuit more.

In the first storage cell charging period, the control circuit may turnon the first coil connection switch and the first storage cell upperside connection switch, and turn off the second coil connection switch,the first to Nth storage cell lower side connection switches, and thesecond to (N−1) th storage cell upper side connection switches; in theMth coil charging period, the control circuit may turn on the first andsecond coil connection switches, and turn off the first to Nth storagecell lower side connection switches and the first to (N−1)th storagecell upper side connection switches; and in the Mth storage cellcharging period, the control circuit may turn off the first and secondcoil connection switches, turn on the Mth storage cell lower sideconnection switch and the Mth storage cell upper side connection switch,and turn off the switches other than the Mth storage cell lower sideconnection switch among the first to Nth storage cell lower sideconnection switches, and the switches other than the Mth storage cellupper side connection switch among the first to (N−1)th storage cellupper side connection switches. By employing this configuration, it isnot necessary to provide a plurality of coils and it is possible todownsize a whole configuration of the balance charging circuit more.

In the first coil charging period, the control circuit may turn on thefirst storage cell upper side connection switch instead of turning onthe second coil connection switch. By employing this configuration, itis not necessary to provide a plurality of coils and it is possible todownsize a whole configuration of the balance charging circuit more.

In the kth coil charging period, the control circuit may turn on thefirst and second coil connection switches, and turn off the first to Nthstorage cell lower side connection switches and the first to (N−1)thstorage cell upper side connection switches; in the first storage cellcharging period, the control circuit may turn on the first coilconnection switch and the first storage cell upper side connectionswitch, and turn off the second coil connection switch, the first to Nthstorage cell lower side connection switches, and the switches other thanthe first storage cell upper side connection switch among the first to(N−1)th storage cell upper side connection switches; and in the kth(k≧2) storage cell charging period, the control circuit may turn off thefirst and second coil connection switches, turn on the kth storage celllower side connection switch and the kth storage cell upper sideconnection switch, and turn off the switches other than the kth storagecell lower side connection switch among the first to Nth storage celllower side connection switches, and the switches other than the kthstorage cell upper side connection switch among the first to (N−1)thstorage cell upper side connection switches. By employing thisconfiguration, it is not necessary to provide a plurality of coils andit is possible to downsize a whole configuration of the balance chargingcircuit more.

The plurality of first switches may include a first coil connectionswitch having one end connected to the input terminal and another endconnected to one end of the coil, a second coil connection switch havingone end connected to another end of the coil and another end connectedto the reference voltage terminal, a third coil connection switch havingone end connected to the input terminal and another end connected to theanother end of the coil, and a fourth coil connection switch having oneend connected to the one end of the coil and another end connected tothe reference voltage terminal; and the plurality of second switches mayinclude a kth (k is an even number) storage cell lower side connectionswitch having one end connected to a lower side of each of the first toNth storage cells, and another end connected to the one end of the coil,and a kth (k is an odd number) storage cell upper side connection switchhaving one end connected to an upper side of each of the first to(N−1)th storage cells, and another end connected to the one end of thecoil. By employing this configuration, it is not necessary to provide aplurality of coils and it is possible to downsize a whole configurationof the balance charging circuit more.

In the kth (k is an odd number) coil charging period, the controlcircuit may turn on the first and second coil connection switches, andturn off the first to Nth storage cell lower side connection switchesand the first to (N−1)th storage cell upper side connection switches; inthe kth (k is an even number) coil charging period, the control circuitmay turn on the third and fourth coil connection switches, and turn offthe first to Nth storage cell lower side connection switches and thefirst to (N−1)th storage cell upper side connection switches; in the kth(k is an odd number) storage cell charging period, the control circuitmay turn on the kth storage cell upper side connection switch and the(k+1)th storage cell lower side connection switch, turn off the first tofourth coil connection switches, and turn off switches other than thekth storage cell upper side connection switch among the first to (N−1)thstorage cell upper side connection switches and switches other than the(k+1)th storage cell lower side connection switch among the first to Nthstorage cell lower side connection switches; and in the kth (k is aneven number) storage cell charging period, the control circuit may turnon the kth storage cell lower side connection switch and the (k−1)thstorage cell upper side connection switch, turn off the first to fourthcoil connection switches, and turn off switches other than the kthstorage cell lower side connection switch among the first to Nth storagecell lower side connection switches and switches other than the (k−1)thstorage cell upper side connection switch among the first to (N−1)thstorage cell upper side connection switches. By employing thisconfiguration, it is not necessary to provide a plurality of coils andit is possible to downsize a whole configuration of the balance chargingcircuit more.

In the first coil charging period, the control circuit may turn on thefirst storage cell upper side connection switch instead of turning onthe second coil connection switch. By employing this configuration, itis not necessary to provide a plurality of coils and it is possible todownsize a whole configuration of the balance charging circuit more.

In the first coil charging period, the control circuit may turn on thefirst coil connection switch instead of turning on the fourth coilconnection switch. By employing this configuration, it is not necessaryto provide a plurality of coils and it is possible to downsize a wholeconfiguration of the balance charging circuit more.

The plurality of first switches may include a first coil connectionswitch having one end connected to the input terminal and another endconnected to one end of the coil, a third coil connection switch havingone end connected to the input terminal and another end connected toanother end of the coil, and a fourth coil connection switch having oneend connected to the one end of the coil and another end connected tothe reference voltage terminal; and the plurality of second switches mayinclude third to Nth storage cell lower side connection switches eachhaving one end connected to a lower side of each of the third to Nthstorage cells and another end connected to the one end of the coil, andfirst to (N−1)th storage cell upper side connection switches each havingone end connected to an upper side of each of the first to (N−1)thstorage cells and another end connected to the one end of the coil. Byemploying this configuration, it is not necessary to provide a pluralityof coils and it is possible to downsize a whole configuration of thebalance charging circuit more.

In the first coil charging period, the control circuit may turn on thefirst coil connection switch and the first storage cell upper sideconnection switch; in the second to Nth coil charging periods, thecontrol circuit may turn on the third and fourth coil connectionswitches, and turn off the third to Nth storage cell lower sideconnection switches and the first to (N−1)th storage cell upper sideconnection switches; in the first storage cell charging period, thecontrol circuit may turn on the fourth coil connection switch and thefirst storage cell upper side connection switch, and turn off the thirdto Nth storage cell lower side connection switches, and switches otherthan the first storage cell upper side connection switch among the firstto (N−1) th storage cell upper side connection switches; and in the kth(k≧2) storage cell charging period, the control circuit may turn off thefirst to third coil connection switches, turn on the (k+1)th storagecell lower side connection switch and the kth storage cell upper sideconnection switch, and turn off switches other than the (k+1)th storagecell lower side connection switch among the first to Nth storage celllower side connection switches, and switches other than the kth storagecell upper side connection switch among the first to (N−1) th storagecell upper side connection switches. By employing this configuration, itis not necessary to provide a plurality of coils and it is possible todownsize a whole configuration of the balance charging circuit more.

The plurality of first switches may include a first coil connectionswitch having one end connected to the input terminal and another endconnected to one end of the coil, and a fourth coil connection switchhaving one end connected to the one end of the coil and another endconnected to the reference voltage terminal; and the plurality of secondswitches may include third to Nth storage cell lower side connectionswitches each having one end connected to a lower side of each of thethird to Nth storage cells and another end connected to the one end ofthe coil, and first to (N−1)th storage cell upper side connectionswitches each having one end connected to an upper side of each of thefirst to (N−1)th storage cells and another end connected to the one endof the coil. By employing this configuration, it is not necessary toprovide a plurality of coils and it is possible to downsize a wholeconfiguration of the balance charging circuit more.

In the first coil charging period, the control circuit may turn on thefirst coil connection switch and the first storage cell upper sideconnection switch; in the second to Nth coil charging periods, thecontrol circuit may turn on the fourth coil connection switch and thefirst storage cell upper side connection switch, and turn off the thirdto Nth storage cell lower side connection switches and the first to(N−1)th storage cell upper side connection switches; in the firststorage cell charging period, the control circuit may turn on the fourthcoil connection switch and the first storage cell upper side connectionswitch, and turn off the third to Nth storage cell lower side connectionswitches, and switches other than the first storage cell upper sideconnection switch among the first to (N−1)th storage cell upper sideconnection switches; and in the kth (k≧2) storage cell charging period,the control circuit may turn off the first to third coil connectionswitches, turn on the (k+1)th storage cell lower side connection switchand the kth storage cell upper side connection switch, and turn offswitches other than the (k+1)th storage cell lower side connectionswitch among the first to Nth storage cell lower side connectionswitches, and switches other than the kth storage cell upper sideconnection switch among the first to (N−1) th storage cell upper sideconnection switches. By employing this configuration, it is notnecessary to provide a plurality of coils and it is possible to downsizea whole configuration of the balance charging circuit more.

In the kth (2≦k≦N) coil charging period, the control circuit may turn onthe fourth coil connection switch and the (k−1)th storage cell upperside connection switch, and turn off the third to Nth storage cell lowerside connection switches, and switches other than the (k−1)th storagecell upper side connection switch among the second to Nth storage cellupper side connection switches. By employing this configuration, it isnot necessary to provide a plurality of coils and it is possible todownsize a whole configuration of the balance charging circuit more.

The plurality of first switches may include a first coil connectionswitch having one end connected to the input terminal and another endconnected to one end of the coil, and a fourth coil connection switchhaving one end connected to the one end of the coil and another endconnected to the reference voltage terminal; the plurality of secondswitches may include third to Nth storage cell lower side connectionswitches each having one end connected to a lower side of each of thethird to Nth storage cells and another end connected to the one end ofthe coil, and first to (N−1) th storage cell upper side connectionswitches each having one end connected to an upper side of each of thefirst to (N−1) th storage cells and another end connected to the one endof the coil; and the balance charging circuit may further include adiode having a cathode connected to the upper side of the first storagecell and an anode connected to the first storage cell upper sideconnection switch, and a capacitor connected between the anode of thediode and the reference voltage. By employing this configuration, it isnot necessary to provide a plurality of coils and it is possible todownsize a whole configuration of the balance charging circuit more.

The plurality of first switches may include a first coil connectionswitch having one end connected to the input terminal and another endconnected to one end of the coil, and a fourth coil connection switchhaving one end connected to the one end of the coil and another endconnected to the reference voltage terminal; the plurality of secondswitches may include third to Nth storage cell lower side connectionswitches each having one end connected to a lower side of each of thethird to Nth storage cells and another end connected to the one end ofthe coil, and first to (N−1) th storage cell upper side connectionswitches each having one end connected to an upper side of each of thefirst to (N−1)th storage cells and another end connected to the one endof the coil; and the balance charging circuit may further include firstto (N−1) th diodes each provided for each of the first to (N−1) thstorage cells and having a cathode connected to an upper side of acorresponding storage cell and an anode connected to each of the firstto (N−1)th storage cell upper side connection switches, and first to(N−1)th capacitors each provided for each of the first to (N−1)th diodesand connected between an anode of a corresponding diode and a referencevoltage. By employing this configuration, it is not necessary to providea plurality of coils and it is possible to downsize a wholeconfiguration of the balance charging circuit more.

In the first coil charging period, the control circuit may turn on thefirst coil connection switch and the first storage cell upper sideconnection switch; in the second to Nth coil charging periods, thecontrol circuit may turn on the fourth coil connection switch and thefirst storage cell upper side connection switch, and turn off the thirdto Nth storage cell lower side connection switches and the first to(N−1)th storage cell upper side connection switches; in the firststorage-cell charging period, the control circuit may turn on the fourthcoil connection switch and the first storage cell upper side connectionswitch, and turn off the third to Nth storage cell lower side connectionswitches, and switches other than the first storage cell upper sideconnection switch among the first to (N−1)th storage cell upper sideconnection switches; and in the kth (k≧2) storage cell charging period,the control circuit may turn off the first to third coil connectionswitches, turn on the (k+1)th storage cell lower side connection switchand the kth storage cell upper side connection switch, and turn offswitches other than the (k+1)th storage cell lower side connectionswitch among the first to Nth storage cell lower side connectionswitches, and switches other than the kth storage cell upper sideconnection switch among the first to (N−1) th storage cell upper sideconnection switches. By employing this configuration, it is notnecessary to provide a plurality of coils and it is possible to downsizea whole configuration of the balance charging circuit more.

The balance charging circuit may further include a (N+1)th storage celllower side connection switch having one end connected to an upper sideof the Nth storage cell and another end connected to the one end of thecoil, and in a case where the Nth storage cell is charged, the (N+1)thstorage cell lower side connection switch may be turned on together withthe Nth upper-side connection switch. By employing this configuration,it is not necessary to provide a plurality of coils and it is possibleto downsize a whole configuration of the balance charging circuit more.

The plurality of first switches may include a first coil connectionswitch having one end connected to the input terminal and another endconnected to one end of the coil and a second coil connection switchhaving one end connected to another end of the coil and another endconnected to the reference voltage terminal; and the plurality of secondswitches may include first to Nth storage cell lower side connectionswitches each having one end connected to a lower side of each of thefirst to Nth storage cells and another end connected to the one end ofthe coil, and first to Nth storage cell upper side connection switcheseach having one end connected to an upper side of each of the first toNth storage cells and another end connected to the one end of the coil.By employing this configuration, it is not necessary to provide aplurality of coils and it is possible to downsize a whole configurationof the balance charging circuit more.

In the first to Nth coil charging periods, the control circuit may turnon the first coil connection switch and the second coil connectionswitch; and in the kth (1≦k≦N) storage cell charging period, the controlcircuit may turn on the kth storage cell lower side connection switchand the kth storage cell upper side connection switch, and turn offswitches other than the kth storage cell lower side connection switchamong the first to Nth storage cell lower side connection switches, andswitches other than the kth storage cell upper side connection switchamong the first to Nth storage cell upper side connection switches. Byemploying this configuration, it is not necessary to provide a pluralityof coils and it is possible to downsize a whole configuration of thebalance charging circuit more.

After all operations corresponding to the kth (k is an odd number) coilcharging period and the kth (k is an odd number) storage cell chargingperiod are completed, the control circuit may control the switches sothat operations corresponding to the kth (k is an even number) coilcharging period and the kth (k is an even number) storage cell chargingperiod are performed. By employing this configuration, it is notnecessary to provide a plurality of coils and it is possible to downsizea whole configuration of the balance charging circuit more. Further, adirection of a current flowing in the coil is changed only once, so thatefficient power consumption is attained.

The control circuit may control the switches so that an upper side ofthe Pth (P is any of 1 to N) storage cell in the first to Nth storagecells is electrically connected to an upper side of the Qth (Q is any of1 to N except P) storage cell to maintain charging voltage balancebetween the Pth storage cell and the Qth storage cell. By employing thisconfiguration, it is not necessary to provide a plurality of coils andit is possible to downsize a whole configuration of the balance chargingcircuit more. By employing this configuration, it is not necessary toprovide a plurality of coils and it is possible to downsize a wholeconfiguration of the balance charging circuit more.

Further, a balance charging method for series-connected storage cellsaccording to the present invention is a balance charging method forseries-connected storage cells in which a power is supplied from a powersupply connected to an input terminal, and first to Nth (N is an integerof 2 or more, the same applies hereinafter) storage cells connected inseries sequentially from a reference voltage terminal between an outputterminal and the reference voltage terminal are charged in a balancedmanner, and the balance charging method includes: a first step ofelectrically connecting a coil between the input terminal and thereference voltage terminal and charging the coil with a charging currentto charge the kth (1≦k≦N) storage cell; a second step of electricallyconnecting the coil to both ends of the kth storage cell and chargingthe kth storage cell with the charging current charged in the coil inthe first step; and a third step of repeatedly performing the first andsecond steps to charge the first to Nth storage cells one by one. Byemploying this method, it is not necessary to provide a plurality ofcoils and it is possible to charge series-connected storage cells in abalanced manner by a single coil.

Advantageous Effects of the Invention

According to the present invention, a coil for charging series-connectedcells with electric charge and a coil for maintaining voltage balancebetween the series-connected cells can be combined, that is, can berealized by a single coil, thereby yielding an effect that a wholecircuit can be more downsized.

Further, since the series-connected cells are charged while voltagebalance is maintained, it is not necessary to provide another chargingcircuit separately, thereby yielding an effect that a whole circuit canbe more downsized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram illustrating a first embodiment of thepresent invention;

FIG. 2 is a view to explain an operation of the first embodiment of thepresent invention;

FIG. 3 is a view to explain an operation of the first embodiment of thepresent invention;

FIG. 4 is a view to explain an operation of the first embodiment of thepresent invention;

FIG. 5 is a view to explain an operation of the first embodiment of thepresent invention;

FIG. 6 is a view to explain an operation of the first embodiment of thepresent invention;

FIG. 7 is a view illustrating controlled contents of a control circuitaccording to the first embodiment of the present invention;

FIG. 8 is a view illustrating controlled contents of a control circuitaccording to the first embodiment of the present invention;

FIG. 9 is a circuit diagram illustrating a second embodiment of thepresent invention;

FIG. 10 is a view to explain an operation of the second embodiment ofthe present invention;

FIG. 11 is a view to explain an operation of the second embodiment ofthe present invention;

FIG. 12 is a view to explain an operation of the second embodiment ofthe present invention;

FIG. 13 is a view to explain an operation of the second embodiment ofthe present invention;

FIG. 14 is a view illustrating controlled contents of a control circuitaccording to the second embodiment of the present invention;

FIG. 15 is a circuit diagram illustrating a third embodiment of thepresent invention;

FIG. 16 is a view to explain an operation of the third embodiment of thepresent invention;

FIG. 17 is a view to explain an operation of the third embodiment of thepresent invention;

FIG. 18 is a view to explain an operation of the third embodiment of thepresent invention;

FIG. 19 is a view to explain an operation of the third embodiment of thepresent invention;

FIG. 20 is a view illustrating controlled contents of a control circuitaccording to the third embodiment of the present invention;

FIG. 21 is a circuit diagram illustrating a fourth embodiment of thepresent invention;

FIG. 22 is a view to explain an operation of the fourth embodiment ofthe present invention;

FIG. 23 is a view to explain an operation of the fourth embodiment ofthe present invention;

FIG. 24 is a view to explain an operation of the fourth embodiment ofthe present invention;

FIG. 25 is a view to explain an operation of the fourth embodiment ofthe present invention;

FIG. 26 is a view illustrating controlled contents of a control circuitaccording to the fourth embodiment of the present invention;

FIG. 27 is a circuit diagram illustrating a fifth embodiment of thepresent invention;

FIG. 28 is a view to explain an operation of the fifth embodiment of thepresent invention;

FIG. 29 is a view to explain an operation of the fifth embodiment of thepresent invention;

FIG. 30 is a view to explain an operation of the fifth embodiment of thepresent invention;

FIG. 31 is a view to explain an operation of the fifth embodiment of thepresent invention;

FIG. 32 is a view illustrating controlled contents of a control circuitaccording to the fifth embodiment of the present invention;

FIG. 33 is a circuit diagram illustrating a sixth embodiment of thepresent invention;

FIG. 34 is a view to explain an operation of the sixth embodiment of thepresent invention;

FIG. 35 is a view to explain an operation of the sixth embodiment of thepresent invention;

FIG. 36 is a view to explain an operation of the sixth embodiment of thepresent invention;

FIG. 37 is a view to explain an operation of the sixth embodiment of thepresent invention;

FIG. 38 is a view illustrating controlled contents of a control circuitaccording to the sixth embodiment of the present invention;

FIG. 39 is a circuit diagram illustrating a seventh embodiment of thepresent invention;

FIG. 40 is a view to explain an operation of the seventh embodiment ofthe present invention;

FIG. 41 is a view to explain an operation of the seventh embodiment ofthe present invention;

FIG. 42 is a view to explain an operation of the seventh embodiment ofthe present invention;

FIG. 43 is a view to explain an operation of the seventh embodiment ofthe present invention;

FIG. 44 is a view to explain an operation of the seventh embodiment ofthe present invention;

FIG. 45 is a view illustrating controlled contents of a control circuitaccording to the seventh embodiment of the present invention;

FIG. 46 is a circuit diagram illustrating an eighth embodiment of thepresent invention;

FIG. 47 is a view to explain an operation of the eighth embodiment ofthe present invention;

FIG. 48 is a view to explain an operation of the eighth embodiment ofthe present invention;

FIG. 49 is a view to explain an operation of the eighth embodiment ofthe present invention;

FIG. 50 is a view to explain an operation of the eighth embodiment ofthe present invention;

FIG. 51 is a view illustrating controlled contents of a control circuitaccording to the eighth embodiment of the present invention;

FIG. 52 is a circuit diagram illustrating a ninth embodiment of thepresent invention;

FIG. 53 is a view to explain an operation of the ninth embodiment of thepresent invention;

FIG. 54 is a view to explain an operation of the ninth embodiment of thepresent invention;

FIG. 55 is a view to explain an operation of the ninth embodiment of thepresent invention;

FIG. 56 is a view to explain an operation of the ninth embodiment of thepresent invention;

FIG. 57 is a view to explain an operation of the ninth embodiment of thepresent invention;

FIG. 58 is a view to explain an operation of the ninth embodiment of thepresent invention;

FIG. 59 is a view illustrating controlled contents of a control circuitaccording to the ninth embodiment of the present invention;

FIG. 60 is a view illustrating controlled contents of a control circuitaccording to a modification of the ninth embodiment of the presentinvention;

FIG. 61 is a view illustrating controlled contents of a control circuitaccording to the modification of the ninth embodiment of the presentinvention;

FIG. 62 is a view illustrating controlled contents of a control circuitaccording to the modification of the ninth embodiment of the presentinvention;

FIG. 63 is a circuit diagram illustrating a tenth embodiment of thepresent invention;

FIG. 64 is a view to explain an operation of the tenth embodiment of thepresent invention;

FIG. 65 is a view to explain an operation of the tenth embodiment of thepresent invention;

FIG. 66 is a view to explain an operation of the tenth embodiment of thepresent invention;

FIG. 67 is a view to explain an operation of the tenth embodiment of thepresent invention;

FIG. 68 is a view to explain an operation of the tenth embodiment of thepresent invention;

FIG. 69 is a view illustrating controlled contents of a control circuitaccording to the tenth embodiment of the present invention;

FIG. 70 is a circuit diagram illustrating an eleventh embodiment of thepresent invention;

FIG. 71 is a view to explain an operation of the eleventh embodiment ofthe present invention;

FIG. 72 is a view to explain an operation of the eleventh embodiment ofthe present invention;

FIG. 73 is a view to explain an operation of the eleventh embodiment ofthe present invention;

FIG. 74 is a view to explain an operation of the eleventh embodiment ofthe present invention;

FIG. 75 is a view to explain an operation of the eleventh embodiment ofthe present invention;

FIG. 76 is a view illustrating controlled contents of a control circuitaccording to the eleventh embodiment of the present invention;

FIG. 77 is a circuit diagram illustrating a twelfth embodiment of thepresent invention;

FIG. 78 is a view to explain an operation of the twelfth embodiment ofthe present invention;

FIG. 79 is a view to explain an operation of the twelfth embodiment ofthe present invention;

FIG. 80 is a view to explain an operation of the twelfth embodiment ofthe present invention;

FIG. 81 is a view to explain an operation of the twelfth embodiment ofthe present invention;

FIG. 82 is a view to explain an operation of the twelfth embodiment ofthe present invention;

FIG. 83 is a view to explain an operation of the twelfth embodiment ofthe present invention;

FIG. 84 is a view illustrating controlled contents of a control circuitaccording to the twelfth embodiment of the present invention;

FIG. 85 is a circuit diagram illustrating a thirteenth embodiment of thepresent invention;

FIG. 86 is a view to explain an operation of the thirteenth embodimentof the present invention;

FIG. 87 is a view to explain an operation of the thirteenth embodimentof the present invention;

FIG. 88 is a view to explain an operation of the thirteenth embodimentof the present invention;

FIG. 89 is a view to explain an operation of the thirteenth embodimentof the present invention;

FIG. 90 is a view to explain an operation of the thirteenth embodimentof the present invention;

FIG. 91 is a view illustrating controlled contents of a control circuitaccording to the thirteenth embodiment of the present invention;

FIG. 92 is a circuit diagram illustrating a fourteenth embodiment of thepresent invention;

FIG. 93 is a view to explain an operation of the fourteenth embodimentof the present invention;

FIG. 94 is a view to explain an operation of the fourteenth embodimentof the present invention;

FIG. 95 is a view to explain an operation of the fourteenth embodimentof the present invention;

FIG. 96 is a view to explain an operation of the fourteenth embodimentof the present invention;

FIG. 97 is a view to explain an operation of the fourteenth embodimentof the present invention;

FIG. 98 is a view to explain an operation of the fourteenth embodimentof the present invention;

FIG. 99 is a view illustrating controlled contents of a control circuitaccording to the fourteenth embodiment of the present invention;

FIG. 100 is a view illustrating an example of a cell balancing controlat the time of discharge;

FIG. 101 is a view illustrating an example of a cell balancing controlat the time of discharge;

FIG. 102 is a view illustrating an example of a cell balancing controlat the time of discharge;

FIG. 103 is a view illustrating an example of a cell balancing controlat the time of discharge;

FIG. 104 is a view illustrating an example of a cell balancing controlat the time of discharge;

FIG. 105 is a view illustrating an example of a cell balancing controlat the time of discharge;

FIG. 106 is a view illustrating an example of a cell balancing controlat the time of discharge;

FIG. 107 is a view illustrating an example of a cell balancing controlat the time of discharge;

FIG. 108 is a view illustrating an example of a cell balancing controlat the time of discharge;

FIG. 109 is a circuit diagram illustrating a conventional balancecharging circuit for series-connected cells;

FIG. 110 is a view to explain an operation of the conventional balancecharging circuit for series-connected cells;

FIG. 111 is a view to explain an operation of the conventional balancecharging circuit for series-connected cells;

FIG. 112 is a view to explain an operation of the conventional balancecharging circuit for series-connected cells; and

FIG. 113 is a view to explain an operation of the conventional balancecharging circuit for series-connected cells.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described below withreference to drawings. Note that, in each figure to be referred to inthe following description, an equivalent part in other figures isindicated by the same reference sign and an explanation about theequivalent part is omitted appropriately.

(Configuration of Balance Charging Circuit According to FirstEmbodiment)

Firstly explained is a configuration of a balance charging circuit forseries-connected cells according to a first embodiment of the presentinvention. FIG. 1 is a circuit diagram illustrating the first embodimentof the present invention.

The balance charging circuit for series-connected cells according to thefirst embodiment of the present invention includes a coil (an inductor)L1, switches S1 to S6, a control circuit Control 1, a cell Cell1, and acell Cell2. The cell Cell1 and the cell Cell2 are connected in seriesand have one series-connected end connected to an output terminal 102and another series-connected end connected to a reference voltageterminal. One end of the switch S1 is connected to a contact pointbetween the cell Cell1 and the cell Cell2, one end of the switch S2 isconnected to an input terminal 101, one end of the switch S3 isconnected to a reference voltage terminal, one end of the switch S4 isconnected to the output terminal 102, one end of the switch S5 isconnected to the reference voltage terminal, and one end of the switchS6 is connected to the contact point between the cell Cell1 and the cellCell2. Further, one end of the coil L1 is connected to another ends ofthe switches S1 to S3 and another end thereof is connected to anotherends of the switches S4 to S6. Further, the control circuit Control 1 isconnected to control terminals of the switches S1 to S6 so as to controlon and off. The control circuit Control 1 can be realized by, forexample, a sequential circuit using a well-known gate circuit or a PWMsignal generation circuit for generating a PWM signal having a pulsewidth according to a current and a voltage of each cell.

Here, the switches S1 to S6 can be realized by a semiconductor elementsuch as an N-channel MOS transistor, a P-channel MOS transistor, an NPNbipolar transistor, or a PNP bipolar transistor.

In a case where the N-channel MOS transistor or the P-channel MOStransistor is employed as a switch, one end of the switch serves aseither of a source and a drain, and another end thereof serves as theother one of the source and the drain. Further, the control terminalserves as a gate.

In a case where the NPN bipolar transistor or the PNP bipolar transistoris employed as a switch, one end of the switch serves as either of anemitter and a collector, and another end thereof serves as the other oneof the emitter and the collector. Further, the control terminal servesas a base.

In a case where the N-channel MOS transistor or the NPN bipolartransistor is employed as a switch, when a high voltage is applied tothe control terminal, the switch is turned on, and when a low voltage isapplied to the control terminal, the switch is turned off.

In a case where the P-channel MOS transistor or the PNP bipolartransistor is employed as a switch, when a low voltage is applied to thecontrol terminal, the switch is turned on, and when a high voltage isapplied to the control terminal, the switch is turned off.

The control circuit Control 1 receives an output voltage Vout, acontact-point voltage Vmid between the cell Cell1 and the cell Cell2,and a reference voltage Vcom to find both ends voltages of the cellCell1 and the cell Cell2. Further, the control circuit Control 1monitors charging currents respectively flowing in the cell Cell1 andthe cell Cell2 by current monitoring circuits M1 and M2, and receivescurrent values thus monitored. Then, the control circuit Control 1controls on and off times of the switches S1 to S6 based on the bothends voltages thus found and the current values thus monitored so thatthe cell Cell1 and the cell Cell2 are charged in a balanced manner.

The current monitoring circuits M1 and M2 can be realized by a currentsensor using a sense resistor or a current mirror circuit.

(Operation of Balance Charging Circuit According to First Embodiment)

Next, an operation of the balance charging circuit for series-connectedcells according to the first embodiment of the present invention will beexplained. FIGS. 2 to 6 are views to explain operations of the firstembodiment of the present invention.

In the balance charging circuit for series-connected cells according tothe first embodiment of the present invention, in order to chargeseries-connected cells and maintain voltage balance between theseries-connected cells, first to fourth charging periods are set by thecontrol circuit Control 1.

Firstly, in the first charging period, the control circuit Control 1turns on the switch S2 and the switch S6. Next, an input voltage Vin isinput from the input terminal 101, so that a charging current to chargethe cell Cell2 with electric charge is stored in the coil L1. A path ofthe charging current is indicated by a dotted arrow of FIG. 2.

It is to be noted that, in the first charging period, the controlcircuit Control 1 may be configured to turn on the switch S2 and theswitch S5, as illustrated in FIG. 3. Then, an input voltage Vin is inputfrom the input terminal 101, so that a charging current to charge thecell Cell2 with electric charge is stored in the coil L1. A path of thecharging current is indicated by a dotted arrow of FIG. 3.

Subsequently, in the second charging period, the control circuit Control1 turns off the switch S2, and turns on the switch S3 and the switch S6.Then, the cell Cell2 is charged with the charging current charged in thecoil L1. A path of the charging current is indicated by a dotted arrowof FIG. 4.

It is to be noted that, in a case where the control circuit Control 1 isconfigured to turn on the switch S2 and the switch S5 as illustrated inFIG. 3 in the first charging period, the control circuit Control 1 turnsoff the switch S2 and the switch S5 in the second charging period.

After that, in the third charging period, the control circuit Control 1turns off the switch S3 and the switch S6, and turns on the switch S2and the switch S5. Then, a charging current to charge the cell Cell1with electric charge is stored in the coil L1. A path of the chargingcurrent is indicated by a dotted arrow of FIG. 5.

Further, in the fourth charging period, the control circuit Control 1turns off the switch S2 and the switch S5, and turns on the switch S1and the switch S4. Then, the cell Cell1 is charged with the chargingcurrent charged in the coil L1. A path of the charging current isillustrated in FIG. 6.

Here, controlled contents by the control circuit Control 1 are explainedwith reference to FIG. 7. FIG. 7 illustrates which switch, among theswitches S1 to S6 in FIG. 1, the control circuit Control 1 turns on ineach of the first to fourth charging periods T1 to T4. That is, amongthe switches S1 to S6, a switch corresponding to a column indicative of“ON” in the figure is turned into an ON state by the control circuitControl 1, and the other switches are turned into an off state.

As illustrated in FIG. 7, the switches S1 and S6 are turned on in thefirst charging period T1 as described above. Then, the switches S3 andS6 are turned on in the second charging period T2. Further, the switchesS2 and S5 are turned on in the third charging period T3. Furthermore,the switches S1 and S4 are turned on in the fourth charging period T4.

The control circuit Control 1 repeatedly controls the switches S1 to S6to turn on as shown in the first to fourth charging periods T1 to T4described above. Accordingly, it is possible to realize a balancecharging circuit using a single coil L1.

In the meantime, as has been explained with reference to FIG. 3, in acase where the switch S2 and the switch S5 are turned on in the firstcharging period, controlled contents by the control circuit Control 1are those illustrated in FIG. 8. That is, among the switches S1 to S6, aswitch corresponding to a column indicative of “ON” in the figure isturned into an ON state by the control circuit Control 1, and the otherswitches are turned into an off state.

In FIG. 8, the switches S2 and S5 are turned on in the first chargingperiod T1 as described above. Then, the switches S3 and S6 are turned onin the second charging period T2. Further, the switches S2 and S5 areturned on in the third charging period T3. Furthermore, the switches S1and S4 are turned on in the fourth charging period T4.

As described above, in the balance charging circuit for series-connectedcells according to the first embodiment of the present invention, asingle coil for temporarily storing a power supplied from a power sourceis provided in common for the cell Cell1 and the cell Cell2 so as tocharge the cell Cell1 and the cell Cell2. In the first charging periodand the second charging period, the cell Cell2 is charged, and in thethird and fourth charging period, the cell Cell1 is charged. That is,the cell Cell1 and cell Cell2 can be charged independently, andtherefore, by setting times for turning on the switches in the first tofourth charging periods according to a variation between a capacitancevalue of the cell Cell1 and a capacitance value of the cell Cell2, theseries-connected cells can be charged with electric charge and voltagebalance between the series-connected cells can be maintained.

For example, in a case where the capacitance value of the cell Cell1 islarger than the capacitance value of the cell Cell2, times for turningon the switches in the first and second charging periods may be setlonger than times for turning on the switches in the third and fourthcharging periods. On the other hand, in a case where the capacitancevalue of the cell Cell1 is smaller than the capacitance value of thecell Cell2, times for turning on the switches in the first and secondcharging periods may be set shorter than times for turning on theswitches in the third and fourth charging periods. By repeatedly settingthe first to fourth charging periods in turn by the control circuitControl 1, the series-connected cells are charged with electric charge,voltage balance between the series-connected cells is maintained, and anoutput voltage Vout can be obtained from the output terminal 502.

According to the above configuration and operations, in the balancecharging circuit for series-connected cells according to the firstembodiment of the present invention, a coil for chargingseries-connected cells with electric charge and a coil for maintainingvoltage balance between the series-connected cells can be combined, thatis, can be realized by a single coil, thereby yielding an effect that awhole circuit is small in size.

Further, each cell in the series-connected cells is not discharged inany of the first to fourth charging periods, thereby yielding an effectthat the series-connected cells which have a limitation in terms of thenumber of charging times can be charged with electric charge and voltagebalance between the series-connected cells can be maintained.

(Configuration of Balance Charging Circuit According to SecondEmbodiment)

Next, a configuration of a balance charging circuit for series-connectedcells according to a second embodiment of the present invention will beexplained. FIG. 9 is a circuit diagram illustrating the secondembodiment of the present invention.

The balance charging circuit for series-connected cells according to thesecond embodiment of the present invention includes a coil L1, switchesS1 to S5, a control circuit Control 2, a cell Cell1, and a cell Cell2,and the cell Cell1 and the cell Cell2 are connected in series and haveone series-connected end connected to an output terminal 202 and anotherseries-connected end connected to a reference voltage terminal. One endof the switch S1 is connected to the output terminal 202, one end of theswitch S2 is connected to an input terminal 201, one end of the switchS3 is connected to the reference voltage terminal, one end of the switchS4 is connected to the input terminal 201, and one end of the switch S5is connected to a contact point between the cell Cell1 and the cellCell2. Further, one end of the coil L1 is connected to another ends ofthe switches S1 to S3 and another end thereof is connected to anotherends of the switches S4 to S5. Further, the control circuit Control 2 isconnected to control terminals of the switches S1 to S5 so as to controlon and off. The control circuit Control 2 can be realized by, forexample, a sequential circuit using a well-known gate circuit or a PWMsignal generation circuit for generating a PWM signal having a pulsewidth according to a current and a voltage of each cell.

Similarly to the balance charging circuit for series-connected cellsaccording to the first embodiment of the present invention, the switchesS1 to S5 can be realized by a semiconductor element such as an N-channelMOS transistor, a P-channel MOS transistor, an NPN bipolar transistor,or a PNP bipolar transistor.

In a case where the N-channel MOS transistor or the P-channel MOStransistor is employed as a switch, one end of the switch serves aseither of a source and a drain, and another end thereof serves as theother one of the source and the drain. Further, the control terminalserves as a gate.

In a case where the NPN bipolar transistor or the PNP bipolar transistoris employed as a switch, one end of the switch serves as either of anemitter and a collector, and another end thereof serves as the other oneof the emitter and the collector. Further, the control terminal servesas a base.

In a case where the N-channel MOS transistor or the NPN bipolartransistor is employed as a switch, when a high voltage is applied tothe control terminal, the switch is turned on, and when a low voltage isapplied to the control terminal, the switch is turned off.

In a case where the P-channel MOS transistor or the PNP bipolartransistor is employed as a switch, when a low voltage is applied to thecontrol terminal, the switch is turned on, and when a high voltage isapplied to the control terminal, the switch is turned off.

The control circuit Control 2 receives an output voltage Vout, acontact-point voltage Vmid between the cell Cell1 and the cell Cell2,and a reference voltage Vcom to find both ends voltages of the cellCell1 and the cell Cell2. Further, the control circuit Control 2monitors charging currents respectively flowing in the cell Cell1 andthe cell Cell2 by current monitoring circuits M1 and M2, and receivescurrent values thus monitored. Then, the control circuit Control 2controls on and off times of the switches S1 to S5 based on the bothends voltages thus found and the current values thus monitored so thatthe cell Cell1 and the cell Cell2 are charged in a balanced manner.

The current monitoring circuits M1 and M2 can be realized by a currentsensor using a sense resistor or a current mirror circuit.

(Operation of Balance Charging Circuit According to Second Embodiment)

Next, an operation of the balance charging circuit for series-connectedcells according to the second embodiment of the present invention willbe explained. FIGS. 10 to 13 are views to explain operations of thesecond embodiment of the present invention.

In the balance charging circuit for series-connected cells according tothe second embodiment of the present invention, in order to chargeseries-connected cells and maintain voltage balance between theseries-connected cells, first to fourth charging periods are set by thecontrol circuit Control 2.

Firstly, in the first charging period, the control circuit Control 2turns on the switch S2 and the switch S5. Then, an input voltage Vin isinput from the input terminal 201, so that a charging current to chargethe cell Cell2 with electric charge is stored in the coil L1. A path ofthe charging current is indicated by a dotted arrow in FIG. 10.

Subsequently, in the second charging period, the control circuit Control2 turns off the switch S2, and turns on the switch S3 and the switch S5.Then, the cell Cell2 is charged with the charging current stored in thecoil L1. A path of the charging current is indicated by a dotted arrowin FIG. 11.

After that, in the third charging period, the control circuit Control 2turns off the switch S3 and the switch S5, and turns on the switch S3and the switch S4. Then, a charging current to charge the cell Cell1with electric charge is stored in the coil L1. A path of the chargingcurrent is indicated by a dotted arrow in FIG. 12.

Further, in the fourth charging period, the control circuit Control 2turns off the switch S3 and the switch S4, and turns on the switch S1and the switch S5. Then, the cell Cell1 is charged with the chargingcurrent charged in the coil L1. A path of the charging current isillustrated in FIG. 13.

Here, controlled contents by the control circuit Control 2 are explainedwith reference to FIG. 14. This figure illustrates which switch, amongthe switches S1 to S5 in FIG. 9, the control circuit Control 2 turns onin each of the first to fourth charging periods T1 to T4. That is, amongthe switches S1 to S5, a switch corresponding to a column indicative of“ON” in the figure is turned into an ON state by the control circuitControl 2, and the other switches are turned into an off state.

Now, referring to FIG. 14, the switches S1 and S5 are turned on in thefirst charging period T1 as described above. Then, the switches S3 andS5 are turned on in the second charging period T2. Further, the switchesS3 and S4 are turned on in the third charging period T3. Furthermore,the switches S1 and S5 are turned on in the fourth charging period T4.

The control circuit Control 2 repeatedly controls the switches S1 to S5to turn on as shown in the first to fourth charging periods T1 to T4described above. Accordingly, it is possible to realize a balancecharging circuit using a single coil L1.

As described above, in the balance charging circuit for series-connectedcells according to the second embodiment of the present invention, asingle coil for temporarily storing a power supplied from a power sourceis provided in common for the cell Cell1 and the cell Cell2 so as tocharge the cell Cell1 and the cell Cell2. In the first charging periodand the second charging period, the cell Cell2 is charged, and in thethird and fourth charging period, the cell Cell1 is charged. That is,the cell Cell1 and cell Cell2 can be charged independently, andtherefore, by setting times for turning on the switches in the first tofourth charging periods according to a variation between a capacitancevalue of the cell Cell1 and a capacitance value of the cell Cell2, theseries-connected cells can be charged with electric charge and voltagebalance between the series-connected cells can be maintained.

For example, in a case where the capacitance value of the cell Cell1 islarger than the capacitance value of the cell Cell2, times for turningon the switches in the first and second charging periods may be setlonger than times for turning on the switches in the third and fourthcharging periods. On the other hand, in a case where the capacitancevalue of the cell Cell1 is smaller than the capacitance value of thecell Cell2, times for turning on the switches in the first and secondcharging periods may be set shorter than times for turning on theswitches in the third and fourth charging periods. By setting the firstto fourth charging periods repeatedly in turn by the control circuitControl 2, the series-connected cells are charged with electric charge,voltage balance between the series-connected cells is maintained, and anoutput voltage Vout can be obtained from the output terminal 202.Further, if times for turning on the switches in the second and fourthcharging periods are set so that a charging current of the coil L1becomes zero at the end of the second and fourth charging periods, atime for removing a residual current of the coil L1 at the end of thesecond and fourth charging periods can be eliminated at the beginning ofthe first and third charging periods. It is also possible to preventpower attenuation which occurs when a refresh current to a power supplyside flows into a parasitic resistor of each element in a current pathin the first and third charging periods.

According to the above configuration and operations, in the balancecharging circuit for series-connected cells according to the secondembodiment of the present invention, a coil for chargingseries-connected cells with electric charge and a coil for maintainingvoltage balance between the series-connected cells can be combined, thatis, can be realized by a single coil, thereby yielding an effect that awhole circuit is small in size.

Further, the number of switches is one fewer than that of the balancecharging circuit for series-connected cells according to the firstembodiment of the present invention, thereby yielding an effect that thewhole circuit can be further downsized.

Further, each cell in the series-connected cells is not discharged inany of the first to fourth charging periods, thereby also yielding aneffect that the series-connected cells which have a limitation in termsof the number of charging times can be charged with electric charge, andvoltage balance between the series-connected cells can be maintained.

(Configuration of Balance Charging Circuit According to ThirdEmbodiment)

Next, a configuration of a balance charging circuit for series-connectedcells according to a third embodiment of the present invention will beexplained. FIG. 15 is a circuit diagram illustrating the thirdembodiment of the present invention.

The balance charging circuit for series-connected cells according to thethird embodiment of the present invention includes a coil L1, switchesS1 to S3, a control circuit Control 3, a cell Cell1, and a cell Cell2,and the cell Cell1 and the cell Cell2 are connected in series and haveone series-connected end connected to an output terminal 302 and anotherseries-connected end connected to a reference voltage terminal. One endof the switch S1 is connected to the output terminal 302, one end of theswitch S2 is connected to an input terminal 301, and one end of theswitch S3 is connected to the reference voltage terminal. Further, oneend of the coil L1 is connected to another ends of the switches S1 to S3and another end thereof is connected to a contact point between the cellCell1 and the cell Cell2. Further, the control circuit Control 3 isconnected to control terminals of the switches S1 to S3 so as to controlon and off. The control circuit Control 3 can be realized by, forexample, a sequential circuit using a well-known gate circuit or a PWMsignal generation circuit for generating a PWM signal having a pulsewidth according to a current and a voltage of each cell.

Similarly to the balance charging circuit for series-connected cellsaccording to the first embodiment of the present invention, the switchesS1 to S3 can be realized by a semiconductor element such as an N-channelMOS transistor, a P-channel MOS transistor, an NPN bipolar transistor,or a PNP bipolar transistor.

In a case where the N-channel MOS transistor or the P-channel MOStransistor is employed as a switch, one end of the switch serves aseither of a source and a drain, and another end thereof serves as theother one of the source and the drain. Further, the control terminalserves as a gate.

In a case where the NPN bipolar transistor or the PNP bipolar transistoris employed as a switch, one end of the switch serves as either of anemitter and a collector, and another end thereof serves as the other oneof the emitter and the collector. Further, the control terminal servesas a base.

In a case where the N-channel MOS transistor or the NPN bipolartransistor is employed as a switch, when a high voltage is applied tothe control terminal, the switch is turned on, and when a low voltage isapplied to the control terminal, the switch is turned off.

In a case where the P-channel MOS transistor or the PNP bipolartransistor is employed as a switch, when a low voltage is applied to thecontrol terminal, the switch is turned on, and when a high voltage isapplied to the control terminal, the switch is turned off.

The control circuit Control 3 receives an output voltage Vout, acontact-point voltage Vmid between the cell Cell1 and the cell Cell2,and a reference voltage Vcom to find both ends voltages of the cellCell1 and the cell Cell2. Further, the control circuit Control 3monitors charging currents respectively flowing in the cell Cell1 andthe cell Cell2 by current monitoring circuits M1 and M2, and receivescurrent values thus monitored. Then, the control circuit Control 3controls on and off times of the switches S1 to S3 based on the bothends voltages thus found and the current values thus monitored so thatthe cell Cell1 and the cell Cell2 are charged in a balanced manner.

The current monitoring circuits M1 and M2 can be realized by a currentsensor using a sense resistor or a current mirror circuit.

(Operation of Balance Charging Circuit According to Third Embodiment)

Next, an operation of the balance charging circuit for series-connectedcells according to the third embodiment of the present invention will beexplained. FIGS. 16 to 19 are views to explain operations of the thirdembodiment of the present invention.

In the balance charging circuit for series-connected cells according tothe third embodiment of the present invention, in order to chargeseries-connected cells and maintain voltage balance between theseries-connected cells, first to fourth charging periods are set by thecontrol circuit Control 3.

Firstly, in the first charging period, the control circuit Control 3turns on the switch S2. Then, an input voltage Vin is input from theinput terminal 301, so that a charging current to charge the cell Cell2with electric charge is stored in the coil L1. A path of the chargingcurrent is indicated by a dotted arrow in FIG. 16.

Subsequently, in the second charging period, the control circuit Control3 turns off the switch S2 and turns on the switch S3. Then, the cellCell2 is charged with the charging current charged in the coil L1. Apath of the charging current is indicated by a dotted arrow in FIG. 17.

After that, in the third charging period, the control circuit Control 3turns on the switch S3. Then, a charging current to charge the cellCell1 with electric charge is stored in the coil L1 from the cell Cell2.A path of the charging current is indicated by a dotted arrow in FIG.18.

Further, in the fourth charging period, the control circuit Control 3turns off the switch S3 and turns on the switch S1. Then, the cell Cell1is charged with the charging current stored in the coil L1. A path ofthe charging current is illustrated in FIG. 19.

Here, controlled contents by the control circuit Control 3 are explainedwith reference to FIG. 20. This figure illustrates which switch, amongthe switches S1 to S3 in FIG. 15, the control circuit Control 3 turns onin each of the first to fourth charging periods T1 to T4. That is, amongthe switches S1 to S3, a switch corresponding to a column indicative of“ON” in the figure is turned into an ON state by the control circuitControl 3, and the other switches are turned into an off state.

As illustrated in FIG. 20, the switch S2 is turned on in the firstcharging period T1 as described above. Then, the switch S3 is turned onin the second charging period T2. Further, the switch S3 is turned on inthe third charging period T3. Furthermore, the switch S1 is turned on inthe fourth charging period T4.

The control circuit Control 3 repeatedly controls the switches S1 to S3to turn on as shown in the first to fourth charging periods T1 to T4described above. Accordingly, it is possible to realize a balancecharging circuit using a single coil L1.

As described above, in the balance charging circuit for series-connectedcells according to the third embodiment of the present invention, asingle coil for temporarily storing a power supplied from a power sourceis provided in common for the cell Cell1 and the cell Cell2 so as tocharge the cell Cell1 and the cell Cell2. In the first charging periodand the second charging period, the cell Cell2 is charged, and in thethird and fourth charging period, the cell Cell1 is charged. That is,the cell Cell1 and cell Cell2 can be charged independently, andtherefore, by setting times for turning on the switches in the first tofourth charging periods according to a variation between a capacitancevalue of the cell Cell1 and a capacitance value of the cell Cell2, theseries-connected cells can be charged with electric charge and voltagebalance between the series-connected cells can be maintained.

For example, in a case where the capacitance value of the cell Cell1 islarger than the capacitance value of the cell Cell2, times for turningon the switches in the first and second charging periods may be setlonger than times for turning on the switches in the third and fourthcharging periods. On the other hand, in a case where the capacitancevalue of the cell Cell1 is smaller than the capacitance value of thecell Cell2, times for turning on the switches in the first and secondcharging periods may be set shorter than times for turning on theswitches in the third and fourth charging periods. By setting the firstto fourth charging periods repeatedly in turn by the control circuitControl 3, the series-connected cells can be charged with electriccharge, voltage balance between the series-connected cells can bemaintained, and an output voltage Vout can be obtained from the outputterminal 302. Further, if times for turning on the switches in thesecond and fourth charging periods are set so that a charging current ofthe coil L1 becomes zero at the end of the second and fourth chargingperiods, a time for removing a residual current of the coil L1 at theend of the second and fourth charging periods can be eliminated at thebeginning of the first and third charging periods. It is also possibleto prevent power attenuation which occurs when a refresh current to apower supply side flows into a parasitic resistor of each element in acurrent path of the first and third charging periods.

According to the above configuration and operations, in the balancecharging circuit for series-connected cells according to the thirdembodiment of the present invention, a coil for chargingseries-connected cells with electric charge and a coil for maintainingvoltage balance between the series-connected cells can be combined, thatis, can be realized by a single coil, thereby yielding an effect that awhole circuit is small in size.

Further, the number of switches is two fewer than that of the balancecharging circuit for series-connected cells according to the secondembodiment of the present invention, thereby yielding an effect that thewhole circuit can be further downsized.

(Configuration of Balance Charging Circuit According to FourthEmbodiment)

Next, a configuration of a balance charging circuit for series-connectedcells according to a fourth embodiment of the present invention will beexplained. FIG. 21 is a circuit diagram illustrating the fourthembodiment of the present invention.

The balance charging circuit for series-connected cells according to thefourth embodiment of the present invention includes a coil L1, switchesS1 to S3, a control circuit Control 4, a capacitor C1, a diode D1, acell Cell1, and a cell Cell2, and the cell Cell1 and the cell Cell2 areconnected in series and have one series-connected end connected to anoutput terminal 402 and another series-connected end connected to areference voltage terminal. One end of the switch S1 is connected to theoutput terminal 402, one end of the switch S2 is connected to an inputterminal 401, and one end of the switch S3 is connected to the referencevoltage terminal. Further, one end of the capacitor C1 is connected tothe reference voltage terminal and a cathode of the diode D1 isconnected to a contact point between the cell Cell1 and the cell Cell2.One end of the coil L1 is connected to another ends of the switches S1to S3 and another end thereof is connected to another end of thecapacitor C1 and an anode of the diode D1. Further, the control circuitControl 4 is connected to control terminals of the switches S1 to S3 soas to control on and off. The control circuit Control 4 can be realizedby, for example, a sequential circuit using a well-known gate circuit ora PWM signal generation circuit for generating a PWM signal having apulse width according to a current and a voltage of each cell.

Similarly to the balance charging circuit for series-connected cellsaccording to the first embodiment of the present invention, the switchesS1 to S3 can be realized by a semiconductor element such as an N-channelMOS transistor, a P-channel MOS transistor, an NPN bipolar transistor,or a PNP bipolar transistor.

In a case where the N-channel MOS transistor or the P-channel MOStransistor is employed as a switch, one end of the switch serves aseither of a source and a drain, and another end thereof serves as theother one of the source and the drain. Further, the control terminalserves as a gate.

In a case where the NPN bipolar transistor or the PNP bipolar transistoris employed as a switch, one end of the switch serves as either of anemitter and a collector, and another end thereof serves as the other oneof the emitter and the collector. Further, the control terminal servesas a base.

In a case where the N-channel MOS transistor or the NPN bipolartransistor is employed as a switch, when a high voltage is applied tothe control terminal, the switch is turned on, and when a low voltage isapplied to the control terminal, the switch is turned off.

In a case where the P-channel MOS transistor or the PNP bipolartransistor is employed as a switch, when a low voltage is applied to thecontrol terminal, the switch is turned on, and when a high voltage isapplied to the control terminal, the switch is turned off.

The control circuit Control 4 receives an output voltage Vout, acontact-point voltage Vmid between the cell Cell1 and the cell Cell2,and a reference voltage Vcom to find both ends voltages of the cellCell1 and the cell Cell2. Further, the control circuit Control 4monitors charging currents respectively flowing in the cell Cell1 andthe cell Cell2 by current monitoring circuits M1 and M2, and receivescurrent values thus monitored. Then, the control circuit Control 4controls on and off times of the switches S1 to S3 based on the bothends voltages thus found and the current values thus monitored so thatthe cell Cell1 and the cell Cell2 are charged in a balanced manner.

The current monitoring circuits M1 and M2 can be realized by a currentsensor using a sense resistor or a current mirror circuit.

Further, the diode D1 can be realized by a PN junction diode, a Schottkybarrier diode, or the like.

(Operation of Balance Charging Circuit According to Fourth Embodiment)

Next, an operation of the balance charging circuit for series-connectedcells according to the fourth embodiment of the present invention willbe explained. FIGS. 22 to 25 are views to explain operations of thefourth embodiment of the present invention.

In the balance charging circuit for series-connected cells according tothe fourth embodiment of the present invention, in order to chargeseries-connected cells and maintain voltage balance between theseries-connected cells, first to fourth charging periods are set by thecontrol circuit Control 4.

Firstly, in the first charging period, the control circuit Control 4turns on the switch S2. Then, an input voltage Vin is input from theinput terminal 401, so that a charging current to charge the capacitorC1 and the cell Cell2 with electric charge is stored in the coil L1. Apath of the charging current is indicated by a dotted arrow in FIG. 22.Subsequently, in the second charging period, the control circuit Control4 turns off the switch S2 and turns on the switch S3. Then, thecapacitor C1 and the cell Cell2 are charged with the charging currentcharged in the coil L1. A path of the charging current is indicated by adotted arrow of FIG. 23.

After that, in the third charging period, the control circuit Control 4turns on the switch S3. Then, a charging current to charge the cellCell1 with electric charge is stored in the coil L1 from the capacitorC1. At this time, the electric charge of the cell Cell2 is maintainedwithout flowing into a side of the coil L1, due to a backflow preventionfunction of the diode D1. A path of the charging current is indicated bya dotted arrow of FIG. 24.

Further, in the fourth charging period, the control circuit Control 4turns off the switch S3 and turns on the switch S1. Then, the cell Cell1is charged with the charging current charged in the coil L1. A path ofthe charging current is illustrated in FIG. 25.

Here, controlled contents by the control circuit Control 4 are explainedwith reference to FIG. 26. This figure illustrates which switch, amongthe switches S1 to S3 in FIG. 21, the control circuit Control 4 turns onin each of the first to fourth charging periods T1 to T4. That is, amongthe switches S1 to S3, a switch corresponding to a column indicative of“ON” in the figure is turned into an ON state by the control circuitControl 4, and the other switches are turned into an off state.

As illustrated in FIG. 26, the switch S2 is turned on in the firstcharging period T1 as described above. Then, the switch S3 is turned onin the second charging period T2. Further, the switch S3 is turned on inthe third charging period T3. Furthermore, the switch S1 is turned on inthe fourth charging period T4.

The control circuit Control 4 repeatedly controls the switches S1 to S3to turn on as shown in the first to fourth charging periods T1 to T4described above. Accordingly, it is possible to realize a balancecharging circuit using a single coil L1.

As described above, in the balance charging circuit for series-connectedcells according to the fourth embodiment of the present invention, asingle coil for temporarily storing a power supplied from a power sourceis provided in common for the cell Cell1 and the cell Cell2 so as tocharge the cell Cell1 and the cell Cell2. In the first charging periodand the second charging period, the cell Cell2 is charged, and in thethird and fourth charging period, the cell Cell1 is charged. That is,the cell Cell1 and cell Cell2 can be charged independently, andtherefore, by setting times for turning on the switches in the first tofourth charging periods according to a variation between a capacitancevalue of the cell Cell1 and a capacitance value of the cell Cell2, theseries-connected cells can be charged with electric charge and voltagebalance between the series-connected cells can be maintained.

For example, in a case where the capacitance value of the cell Cell1 islarger than the capacitance value of the cell Cell2, times for turningon the switches in the first and second charging periods may be setlonger than times for turning on the switches in the third and fourthcharging periods. On the other hand, in a case where the capacitancevalue of the cell Cell1 is smaller than the capacitance value of thecell Cell2, times for turning on the switches in the first and secondcharging periods may be set shorter than times for turning on theswitches in the third and fourth charging periods. By setting the firstto fourth charging periods repeatedly in turn by the control circuitControl 4, the series-connected cells can be charged with electriccharge, voltage balance between the series-connected cells can bemaintained, and an output voltage Vout can be obtained from the outputterminal 402. Further, if times for turning on the switches in thesecond and fourth charging periods are set so that a charging current ofthe coil L1 becomes zero at the end of the second and fourth chargingperiods, a time for removing a residual current of the coil L1 at theend of the second and fourth charging periods can be eliminated at thebeginning of the first and third charging periods. It is also possibleto prevent power attenuation which occurs when a refresh current to apower supply side flows into a parasitic resistor of each element in acurrent path of the first and third charging periods.

According to the above configuration and operations, in the balancecharging circuit for series-connected cells according to the fourthembodiment of the present invention, a coil for chargingseries-connected cells with electric charge and a coil for maintainingvoltage balance between the series-connected cells can be combined, thatis, can be realized by a single coil, thereby yielding an effect that awhole circuit is small in size.

Further, each cell in the series-connected cells is not discharged inany of the first to fourth charging periods, thereby yielding an effectthat the series-connected cells which have a limitation in terms of thenumber of charging times can be charged with electric charge and voltagebalance between the series-connected cells can be maintained.

(In Case where Three or more Cells are Arranged)

The above description, however, has been given of cases where the numberN of storage cells connected in series is “2”, but the number N ofstorage cells may be an integer of “3” or more.

A case where the number N of storage cells is 3 or more (N≧3) will bedescribed. In the following description given with reference torespective figures, the control circuit and the current monitoringcircuits are not illustrated from the convenience of drawing figures.That is, in each figure to be referred to in the following explanation,a control circuit, not illustrated, is provided at a lower side in thefigure, similarly to the above cases. Further, in each figure to bereferred to in the following explanation, a current monitoring circuit,not illustrated, is provided between respective storage cells, similarlyto the above cases.

The control circuit, not illustrated, receives an output voltage Vout,contact-point voltages Vmid1 to VmidN−1 between adjacent cells, and areference voltage Vcom so as to find both ends voltages between thecells. Further, the control circuit, not illustrated, monitors chargingcurrents flowing in respective cells by current monitoring circuitswhich are not illustrated herein, and receives current values thusmonitored. Then, the control circuit, not illustrated, controls on andoff times of respective switches based on the both ends voltages thusfound and the current values thus monitored so that the respective cellsare charged in a balanced manner. The current monitoring circuits whichare not illustrated herein can be realized by a current sensor using asense resistor or a current mirror circuit.

Similarly to the balance charging circuit for series-connected cellsaccording to the first embodiment of the present invention, therespective switches used in explanation of the following embodiments canbe realized by a semiconductor element such as an N-channel MOStransistor, a P-channel MOS transistor, an NPN bipolar transistor, or aPNP bipolar transistor.

In a case where the N-channel MOS transistor or the P-channel MOStransistor is employed as a switch, one end of the switch serves aseither of a source and a drain, and another end thereof serves as theother one of the source and the drain. Further, the control terminalserves as a gate.

In a case where the NPN bipolar transistor or the PNP bipolar transistoris employed as a switch, one end of the switch serves as either of anemitter and a collector, and another end thereof serves as the other oneof the emitter and the collector. Further, the control terminal servesas a base.

In a case where the N-channel MOS transistor or the NPN bipolartransistor is employed as a switch, when a high voltage is applied tothe control terminal, the switch is turned on, and when a low voltage isapplied to the control terminal, the switch is turned off.

In a case where the P-channel MOS transistor or the PNP bipolartransistor is employed as a switch, when a low voltage is applied to thecontrol terminal, the switch is turned on, and when a high voltage isapplied to the control terminal, the switch is turned off.

The control circuit, not illustrated, turns on a given switch pairconnected to both ends of the coil L1 to charge the coil L1 with acurrent, and then turns on another switch pair connected to both ends ofthe coil L1 and a storage cell which pair is different from the aboveswitches, so as to charge the storage cell with the current in the coilL1. Further, the control circuit, not illustrated, monitors voltages ofthe respective storage cells by the current monitoring circuits whichare not illustrated herein, so as to control on and off times of theswitch pairs so that the voltages of the respective storage cells areequal to each other.

(Configuration of Balance Charging Circuit According to FifthEmbodiment)

FIG. 27 is a circuit diagram illustrating an exemplary configuration ofa balance charging circuit for charging, by use of a single coil L1, Npieces of storage cells Cell1 to CellN which are connected in series. InFIG. 27, the balance charging circuit includes a single coil L1, aswitch group SW1 for electrically connecting the coil L1 between aninput terminal 101 into which a charging voltage is input and areference voltage terminal, and a switch group SW2 for electricallyconnecting both ends of each of the storage cells Cell1 to CellN to bothends of the coil L1.

The switch group SW1 includes a switch Sa1 and a switch Sa2, and aswitch Sb1 and a switch Sb2. One ends of the switch Sa1 and the switchSa2 are connected to the input terminal 101, and another ends thereofare respectively connected to one end and another end of the coil L1.One ends of the switch Sb1 and the switch Sb2 are connected to thereference voltage terminal, and another ends thereof are respectivelyconnected to one end and another end of the coil L1.

The switch group SW2 includes switches Sc1 to ScN+1 and switches Sd1 toSdN+1. One ends of the switches Sc1 to ScN+1 are connected to contactpoints of N pieces of the storage cells Cell1 to CellN, an outputterminal 102, and the reference voltage terminal, and another endsthereof are connected to one end of the coil L1. One ends of theswitches Sd1 to SdN+1 are connected to contact points of N pieces of thestorage cells Cell1 to CellN, the output terminal 102, and the referencevoltage terminal, and another ends thereof are connected to another endof the coil L1.

(Operation of Balance Charging Circuit According to Fifth Embodiment)

Next, an operation of the balance charging circuit for series-connectedcells according to the fifth embodiment of the present invention will beexplained. The balance charging circuit for series-connected cellsaccording to the present embodiment is a charge/discharge circuit whichturns on a given switch pair connected to both ends of the coil L1 tocharge the coil L1 with a current, and then turns on another switch pairconnected to both ends of the coil L1 and a storage cell which pair isdifferent from the above switch pair, so as to charge the storage cellwith the current in the coil L1. The balance charging circuit monitorsvoltages of respective storage cells and controls on and off times ofthe switch pairs so that the voltages of the respective storage cellsare equal to each other.

FIGS. 28 to 32 are views to explain operations of the fifth embodimentof the present invention.

In the balance charging circuit for series-connected cells according tothe fifth embodiment of the present invention, in order to chargeseries-connected storage cells and maintain voltage balance between theseries-connected cells, first to Nth charging periods are set by acontrol circuit which is not illustrated in the figure. A first half ofeach of the first to Nth charging periods is a coil charging period(which applies in each of the following embodiments). A second half ofeach of the first to Nth charging periods is a storage cell chargingperiod (which is applies in each of the following embodiments).

Firstly, in a first half of the first charging period, the controlcircuit, not illustrated, turns on switches Sa1 and Sb1. Then, an inputvoltage Vin is input from the input terminal 101, and a charging currentto charge the cell Cell1 is stored in the coil L1. A path of thecharging current is indicated by a dotted arrow of FIG. 28.

Next, in a second half of the first charging period, the controlcircuit, not illustrated, turns off the switches Sa1 and Sb1 and turnson switches Sc1 and Sd2. Then, the cell Cell1 is charged with thecharging current charged in the coil L1. A path of the charging currentis indicated by a dotted arrow of FIG. 29.

After that, in a first half of the second charging period, the controlcircuit, not illustrated, turns off the switches Sc1 and Sd2 and turnson the switches Sa1 and Sb1. Then, an input voltage Vin is input fromthe input terminal 101, and a charging current to charge the cell Cell2is stored in the coil L1. This state is the same as the state in FIG.28, and a path of the charging current is indicated by the dotted arrowof FIG. 28.

Next, in a second half of the second charging period, the switches Sa1and Sb1 are turned off and switches Sc2 and Sd3 are turned on. Then, thecell Cell2 is charged with the charging current charged in the coil L1.A path of the charging current is indicated by a dotted arrow in FIG.30.

Thereafter, a similar operation is repeated to turn on the switches Sa1and Sb1 in a first half of each charging period, so as to store, in thecoil L1, a charging current to charge a storage cell with electriccharge. Then, corresponding switches for both ends of each cell areturned on in a second half of the each charging period, so as to chargethe cell with the charging current stored in the coil L1. Accordingly,in a case where the cell CellN is charged, switches ScN and SdN+1 areturned on. A path of the charging current in this state is indicated bya dotted arrow in FIG. 31.

Here, controlled contents by the control circuit, not illustrated, areexplained with reference to FIG. 32. FIG. 32 illustrates which switch,among the switches in FIG. 27, the control circuit, not illustrated,turns on in each of the first to Nth charging periods T1 to TN. That is,among the switches, a switch corresponding to a column indicative of“ON” in the figure is turned into an ON state by the control circuit,not illustrated, and the other switches are turned into an off state.

As illustrated in FIG. 32, the switches Sa1 and Sb1 are turned on in thefirst half of each of the charging periods T1 to TN, as described above.Then, corresponding switches for both ends of each cell are turned on inthe second half of the each of the charging periods T1 to TN, asdescribed above. As described, the control circuit, not illustrated,repeatedly controls each of the switches to turn on as shown in thefirst to Nth charging periods T1 to TN described above. Accordingly, itis possible to realize a balance charging circuit using a single coilL1.

(Configuration of Balance Charging Circuit According to SixthEmbodiment)

FIG. 33 is a circuit diagram illustrating an exemplary configuration ofa balance charging circuit for charging, by use of a single coil L1, Npieces of storage cells Cell1 to CellN which are connected in series. InFIG. 33, the balance charging circuit includes a single coil L1, aswitch group SW1 for electrically connecting the coil L1 between aninput terminal 101 into which a charging voltage is input and areference voltage terminal, and a switch group SW2 for electricallyconnecting both ends of each of the storage cells Cell1 to CellN to bothends of the coil L1. The configuration of the balance charging circuitof FIG. 33 is a configuration of a balance charging circuit in a casewhere the number of cells is N in the configurations of FIGS. 1 and 8.

The switch group SW1 includes a switch Sa1 and a switch Sb1. One end ofthe switch Sa1 is connected to the input terminal 101, and another endthereof is connected to one end of the coil L1. One end of the switchSb1 is connected to the reference voltage terminal, and another endthereof is connected to another end of the coil L1.

The switch group SW2 includes switches Sc1 to ScN and switches Sd1 toSdN+1. One ends of the switches Sc1 to ScN are connected to contactpoints of N pieces of the storage cells Cell1 to CellN and the referencevoltage terminal, and another ends thereof are connected to the one endof the coil L1. One ends of the switches Sd2 to SdN+1 are connected tothe contact points of N pieces of the storage cells Cell1 to CellN andan output terminal 102, and another ends thereof are connected to theanother end of the coil L1.

As described, the balance charging circuit according to the presentembodiment includes switches as many as the number equal to twice thenumber of storage cells plus “2.” That is, the switches as many as thenumber equal to twice the number of storage cells plus “2” include theswitch group SW2 including 2N pieces of switches for connecting bothends of each storage cell to the coil L1, and the switch group SW1including switch pairs for connecting both ends of the coil L1 betweenthe input terminal and the reference voltage terminal.

A charging period of a control circuit which is not illustrated in thefigure includes a period TJa (J=1 to N) in which the switch Sa1 forconnecting one end of the coil to a charging power input terminal (Vin)and the switch Sb1 for connecting another end of the coil to thereference voltage terminal (Vcom) are turned on, and a period TJb (J=1to N) in which a switch SdJ+1 for connecting a high voltage terminal ofa Jth storage cell to the another end of the coil and a switch ScJ forconnecting a low voltage terminal of the Jth storage cell to the one endof the coil are turned on. Voltages of respective storage cells aremonitored and lengths of the periods T1 a to TNa and lengths of theperiods T1 b to TNb are controlled so that the voltages of therespective storage cells are equal to each other.

A discharge period of the control circuit, not illustrated, includes aperiod Tx having: a period Txa in which the voltages of the respectivestorage cells are monitored, a high-voltage storage cell of a number Pwhich is counted from the first storage cell and a low-voltage storagecell of a number Q which is counted from the first storage cell areselected independently, a switch (ScP+1) for connecting a high-voltageterminal of the high-voltage storage cell to the one end of the coil anda switch (SdP) for connecting a low-voltage terminal of the high-voltagestorage cell to the another end of the coil are turned on so as tocharge the coil with a current; and a period Txb in which a switch(SdQ+1) for connecting a high-voltage terminal of the low-voltagestorage cell to the another end of the coil and a switch (ScQ) forconnecting a low-voltage terminal of the low-voltage storage cell to theone end of the coil are turned on so as to charge the low-voltagestorage cell with a current stored in the coil. The control circuit, notillustrated, controls lengths of the above periods repeatedly so thatthe voltages of the respective storage cells are equal to each other.

(Operation of Balance Charging Circuit According to Sixth Embodiment)

Next, an operation of the balance charging circuit for series-connectedcells according to the sixth embodiment of the present invention will beexplained. The balance charging circuit for series-connected cellsaccording to the present embodiment includes, as a charging time, aperiod TJa (J=1 to N) in which the switch Sa1 for connecting one end ofthe coil L1 to the charging power input terminal (Vin) and the switchSb1 for connecting another end of the coil L1 to the reference voltageterminal (Vcom) are turned on, and a period TJb (J=1 to N) in which aswitch SdJ+1 for connecting a high-voltage terminal of a Jth storagecell to the another end of the coil L1 and a switch ScJ for connecting alow-voltage terminal of the Jth storage cell to the one end of the coilL1 are turned on, monitors voltages of respective storage cells, andcontrols the lengths of the periods T1 a to TNa and the lengths of theperiods T1 b to TNb so that the voltages of the respective storage cellsare equal to each other. Further, the balance charging circuit forseries-connected cells according to the present embodiment includes, asa discharge time for driving a connected load to the output terminal102, a period Tx having: a period Txa in which the voltages of therespective storage cells are monitored, a high-voltage storage cell of anumber P which is counted from the first storage cell and a low-voltagestorage cell of a number Q which is counted from the first storage cellare selected independently, and a switch (ScP+1) for connecting ahigh-voltage terminal of the high-voltage storage cell to the one end ofthe coil L1 and a switch (SdP) for connecting a low-voltage terminal ofthe high-voltage storage cell to the another end of the coil L1 areturned on so as to charge the coil L1 with a current; and a period Txbin which a switch (SdQ+1) for connecting a high-voltage terminal of thelow-voltage storage cell to the another end of the coil L1 and a switch(ScQ) for connecting a low-voltage terminal of the low-voltage storagecell to the one end of the coil L1 are turned on so as to charge thelow-voltage storage cell with the current flowing in the coil L1. Thebalance charging circuit controls lengths of the above periodsrepeatedly so that the voltages of the respective storage cells areequal to each other.

FIGS. 34 to 38 are views to explain operations of the sixth embodimentof the present invention.

In the balance charging circuit for series-connected cells according tothe sixth embodiment of the present invention, in order to chargeseries-connected storage cells and maintain voltage balance between theseries-connected cells, first to Nth charging periods are set by acontrol circuit which is not illustrated in the figure.

Firstly, in a first half of the first charging period, the controlcircuit, not illustrated, turns on the switches Sa1 and Sb1. Then, aninput voltage Vin is input from the input terminal 101, and a chargingcurrent to charge the cell Cell1 with electric charge is stored in thecoil L1. A path of the charging current is indicated by a dotted arrowin FIG. 34.

Subsequently, in a second half of the first charging period, the controlcircuit, not illustrated, turns off the switches Sa1 and Sb1 and turnson the switches Sc1 and Sd2. Then, the cell Cell1 is charged with thecharging current charged in the coil L1. A path of the charging currentis indicated by a dotted arrow in FIG. 35.

After that, in a first half of the second charging period, the controlcircuit, not illustrated, turns off the switches Sc1 and Sd2 and turnson the switches Sa1 and Sb1. Then, an input voltage Vin is input fromthe input terminal 101, and a charging current to charge the cell Cell2with electric charge is stored in the coil L1. This state is the same asthe state in FIG. 34, and a path of the charging current is indicated bythe dotted arrow of FIG. 34.

Next, in a second half of the second charging period, the switches Sa1and Sb1 are turned off and the switches Sc2 and Sd3 are turned on. Then,the cell Cell2 is charged with the charging current charged in the coilL1. A path of the charging current is indicated by a dotted arrow inFIG. 36.

Thereafter, a similar operation is repeated to turn on the switches Sa1and Sb1 in a first half of each charging period, so as to store, in thecoil L1, a charging current to charge a storage cell with electriccharge. Then, corresponding switches for both ends of each cell areturned on in a second half of the each charging period, so as to chargethe cell with the charging current charged in the coil L1. Accordingly,in a case where the cell CellN is charged, the switches ScN and SdN+1are turned on. A path of the charging current in this state is indicatedby a dotted arrow in FIG. 37.

Here, controlled contents by the control circuit, not illustrated, areexplained with reference to FIG. 38. FIG. 38 illustrates which switch,among the switches in FIG. 33, the control circuit, not illustrated,turns on in each of the first to Nth charging periods T1 to TN. That is,among the switches, a switch corresponding to a column indicative of“ON” in the figure is turned into an ON state by the control circuit,not illustrated, and the other switches are turned into an off state.

As illustrated in FIG. 38, the switches Sa1 and Sb1 are turned on in thefirst half of each of the charging periods T1 to TN, as described above.Then, corresponding switches for both ends of each cell are turned on inthe second half of the each of the charging periods T1 to TN, asdescribed above. As described, the control circuit, not illustrated,repeatedly controls each of the switches to turn on as shown in thefirst to Nth charging periods T1 to TN described above. Accordingly, itis possible to realize a balance charging circuit which performs voltageboost and drop operations by use of a single coil L1.

Further, each cell in the series-connected cells is not discharged inany of the charging periods T1 to TN, thereby also yielding an effectthat the series-connected cells which have a limitation in terms of thenumber of charging times can be charged with electric charge and voltagebalance between the series-connected cells can be maintained.

(Configuration of Balance Charging Circuit According to SeventhEmbodiment)

FIG. 39 is a circuit diagram illustrating an exemplary configuration ofa balance charging circuit for charging, by use of a single coil L1, Npieces of storage cells Cell1 to CellN which are connected in series. InFIG. 39, the balance charging circuit includes a single coil L1, aswitch group SW1 for electrically connecting the coil L1 between aninput terminal 101 into which a charging voltage is input and areference voltage terminal, and a switch group SW2 for electricallyconnecting both ends of each of the storage cells Cell1 to CellN to bothends of the coil L1. The configuration of the balance charging circuitof FIG. 39 is a configuration of a balance charging circuit in a casewhere the number of cells is N in the configurations of FIGS. 1 and 7.

The configuration of the balance charging circuit in FIG. 39 itself issimilar to the configuration of the balance charging circuit explainedwith reference to FIG. 33, but some controlled contents of switchescontrolled by a control circuit, not illustrated, are different, and avoltage drop operation is implemented.

(Operation of Balance Charging Circuit According to Seventh Embodiment)

Next, an operation of the balance charging circuit for series-connectedcells according to the seventh embodiment of the present invention willbe explained. FIGS. 40 to 45 are views to explain operations of thesixth embodiment of the present invention.

In the balance charging circuit for series-connected cells according tothe seventh embodiment of the present invention, in order to chargeseries-connected storage cells and maintain voltage balance between theseries-connected cells, first to Nth charging periods are set by acontrol circuit which is not illustrated in the figure. Note thatswitches to be turned on in the first charging period are different fromthose in the sixth embodiment.

That is, in a first half of the first charging period, the controlcircuit, not illustrated, turns on the switches Sa1 and Sd2. In thisregard, the switches to be turned on herein are different from those inthe sixth embodiment. Then, an input voltage Vin is input from the inputterminal 101, so that the cell Cell1 is charged while a charging currentis stored in the coil L1. A path of the charging current is indicated bya dotted arrow in FIG. 40.

Next, in a second half of the first charging period, the controlcircuit, not illustrated, turns off the switch Sa1 and turns on theswitch Sc1 while the switch Sd2 is being turned on. Then, the cell Cell1is charged with the charging current charged in the coil L1. A path ofthe charging current is indicated by a dotted arrow in FIG. 41.

After that, in a first half of the second charging period, the controlcircuit, not illustrated, turns off the switches Sc1 and Sd2 and turnson the switches Sa1 and Sb1. Then, an input voltage Vin is input fromthe input terminal 101, and a charging current to charge the cell Cell2is stored in the coil L1. A path of the charging current is indicated bya dotted arrow in FIG. 42.

Next, in a second half of the second charging period, the switches Sa1and Sb1 are turned off and the switches Sc2 and Sd3 are turned on. Then,the cell Cell2 is charged with the charging current charged in the coilL1. A path of the charging current is indicated by a dotted arrow inFIG. 43.

Thereafter, a similar operation is repeated to turn on the switches Sa1and Sb1 in a first half of each charging subsequent to the secondcharging period, so as to store, in the coil L1, a charging current tocharge a storage cell with electric charge. Then, corresponding switchesfor both ends of each cell are turned on in a second half of the eachcharging period, so as to charge the cell with the charging currentcharged in the coil L1. Accordingly, in a case where the cell CellN ischarged, the switches ScN and SdN+1 are turned on. A path of thecharging current in this state is indicated by a dotted arrow in FIG.44.

Here, controlled contents by the control circuit, not illustrated, areexplained with reference to FIG. 45. FIG. 45 illustrates which switch,among the switches in FIG. 39, the control circuit, not illustrated,turns on in each of the first to Nth charging periods T1 to TN. That is,among the switches, a switch corresponding to a column indicative of“ON” in the figure is turned into an ON state by the control circuit,not illustrated, and the other switches are turned into an off state.

As illustrated in FIG. 45, in each of the charging periods T1 to TN, theswitches Sa1 and Sd2 are turned on in a first half of the first chargingperiod, and the switches Sa1 and Sb1 are turned on in a first half ofeach of the second charging period and its subsequent charging periods.Then, corresponding switches for both ends of each cell are turned on ina second half of each of the charging periods T1 to TN, as describedabove. As described, the control circuit, not illustrated, repeatedlycontrols each of the switches to turn on as shown in the first to Nthcharging periods T1 to TN described above. Accordingly, it is possibleto realize a balance charging circuit using a single coil L1.

Further, each cell in the series-connected cells is not discharged inany of the charging periods T1 to TN, thereby also yielding an effectthat the series-connected cells which have a limitation in terms of thenumber of charging times can be charged with electric charge and voltagebalance between the series-connected cells can be maintained.

(Configuration of Balance Charging Circuit According to EighthEmbodiment)

FIG. 46 is a circuit diagram illustrating an exemplary configuration ofa balance charging circuit for charging, by use of a single coil L1, Npieces of storage cells Cell1 to CellN which are connected in series. InFIG. 46, the balance charging circuit includes a single coil L1, aswitch group SW1 for electrically connecting the coil L1 between aninput terminal 101 into which a charging voltage is input and areference voltage terminal, and a switch group SW2 for electricallyconnecting both ends of each of the storage cells Cell1 to CellN to bothends of the coil L1.

The configuration of the balance charging circuit in FIG. 46 itself issimilar to the configuration of the balance charging circuit explainedwith reference to FIG. 33, but some controlled contents of switchescontrolled by a control circuit, not illustrated, are different, and avoltage boost operation is implemented.

(Operation of Balance Charging Circuit According to Eighth Embodiment)

Next, an operation of the balance charging circuit for series-connectedcells according to the eighth embodiment of the present invention willbe explained. FIGS. 47 to 51 are views to explain operations of theeighth embodiment of the present invention.

In the balance charging circuit for series-connected cells according tothe eighth embodiment of the present invention, in order to chargeseries-connected storage cells and maintain voltage balance between theseries-connected cells, first to Nth charging periods are set by acontrol circuit which is not illustrated in the figure. Note thatswitches to be turned on in the first charging period are different fromthose in the sixth embodiment.

That is, in a first half of the first charging period, the controlcircuit, not illustrated, turns on switches the Sa1 and Sb1. Then, aninput voltage Vin is input from the input terminal 101, and a chargingcurrent to charge the cell Cell1 with electric charge is stored in thecoil L1. A path of the charging current is indicated by a dotted arrowin FIG. 47.

Next, in a second half of the first charging period, the controlcircuit, not illustrated, turns off the switch Sb1 and turns on theswitch Sd2 while the switch Sa1 is being turned on. Then, the cell Cell1is charged with the charging current charged in the coil L1. A path ofthe charging current is indicated by a dotted arrow in FIG. 48.

After that, in a first half of the second charging period, the controlcircuit, not illustrated, turns off the switch Sd2, and turns on theswitch Sb1 while the switch Sa1 is being turned on. Then, an inputvoltage Vin is input from the input terminal 101, and a charging currentto charge the cell Cell2 with electric charge is stored in the coil L1.This state is the same as the state in FIG. 47, and a path of thecharging current is indicated by the dotted arrow of FIG. 47.

Next, in a second half of the second charging period, the switches Sa1and Sb1 are turned off and the switches Sc2 and Sd3 are turned on. Then,the cell Cell2 is charged with the charging current charged in the coilL1. A path of the charging current is indicated by a dotted arrow inFIG. 49.

Thereafter, a similar operation is repeated to turn on the switches Sa1and Sb1 in a first half of each charging period, so as to store, in thecoil L1, a charging current to charge a storage cell with electriccharge. Then, corresponding switches for both ends of each cell areturned on in a second half of the each charging period, so as to chargethe cell with the charging current charged in the coil L1. Accordingly,in a case where the cell CellN is charged, the switches ScN and SdN+1are turned on. A path of the charging current in this state is indicatedby a dotted arrow in FIG. 50.

Here, controlled contents by the control circuit, not illustrated, areexplained with reference to FIG. 51. FIG. 51 illustrates which switch,among the switches in FIG. 46, the control circuit, not illustrated,turns on in each of the first to Nth charging periods T1 to TN. That is,among the switches, a switch corresponding to a column indicative of“ON” in the figure is turned into an ON state by the control circuit,not illustrated, and the other switches are turned into an off state.

As illustrated in FIG. 51, the switches Sa1 and Sb1 are turned on in afirst half of each of the charging periods T1 to TN, as described above.Then, in each of the charging periods T1 to TN, the switches Sa1 and Sd2are turned on in a second half of the first charging period, andcorresponding switches for both end of each cell are turned on in asecond half of each of the second charging period and its subsequentcharging periods. As described, the control circuit, not illustrated,repeatedly controls each of the switches to turn on as shown in thefirst to Nth charging periods T1 to TN described above. Accordingly, itis possible to realize a balance charging circuit using a single coilL1.

Further, each cell in the series-connected cells is not discharged inany of the charging periods T1 to TN, thereby also yielding an effectthat the series-connected cells which have a limitation in terms of thenumber of charging times can be charged with electric charge and voltagebalance between the series-connected cells can be maintained.

(Configuration of Balance Charging Circuit According to NinthEmbodiment)

FIG. 52 is a circuit diagram illustrating an exemplary configuration ofa balance charging circuit for charging, by use of a single coil L1, Npieces of storage cells Cell1 to CellN which are connected in series. InFIG. 52, the balance charging circuit includes a single coil L1, aswitch group SW1 for electrically connecting the coil L1 between aninput terminal 101 into which a charging voltage is input and areference voltage terminal, and a switch group SW2 for electricallyconnecting both ends of each of the storage cells Cell1 to CellN to bothends of the coil L1.

The switch group SW1 includes a switch Sa1 and a switch Sa2, and aswitch Sf0 and a switch Sb1. One ends of the switch Sa1 and the switchSa2 are connected to the input terminal 101, and another ends thereofare respectively connected to one end and another end of the coil L1.One ends of the switch Sf0 and the switch Sb1 are connected to thereference voltage terminal, and another ends thereof are respectivelyconnected to the one end and the other end of the coil L1.

The switch group SW2 includes switches Sf1 to SfN. One ends ofodd-numbered switches Sf1, Sf3, . . . , SfN−1 among the switches Sf1 toSfN are connected to contact points of N pieces of the storage cellsCell1 to CellN, and another ends thereof are connected to the anotherend of the coil L1. One ends of even-numbered switches Sf2, Sf4, . . . ,SfN among the switches Sf1 to SfN are connected to the contact points ofN pieces of the storage cells Cell1 to CellN and the output terminal102, and another ends thereof are connected to the one end of the coilL1.

As described, the balance charging circuit according to the presentembodiment includes switches as many as the number equal to the numberof storage cells plus “4.” That is, the switches as many as the numberequal to the number of storage cells plus “4” include: the switch groupSW2 including N pieces of switches for connecting both ends of eachstorage cell to the coil L1; and the switch group SW1 including fourswitches for connecting the input terminal 101 and the coil L1. Theswitch group SW2 includes switches Sf2 to SfM (switches Sf2, Sf4, . . ., SfM (M is the largest even number which is not more than N) connectedto even-numbered storage cells) for connecting even-numberedhigh-voltage terminals counted from a first storage cell to the one endof the coil, and switches Sf1 to Sf1 (switches Sf1, Sf3, . . . , Sf1 (Lis the largest odd number which is not more than N) connected toodd-numbered storage cells) for connecting odd-numbered high-voltageterminals counted from the first storage cell to the another end of thecoil.

(Operation of Balance Charging Circuit According to Ninth Embodiment)

Next, an operation of the balance charging circuit for series-connectedcells according to the ninth embodiment of the present invention will beexplained. FIGS. 53 to 58 are views to explain operations of the ninthembodiment of the present invention.

In the balance charging circuit for series-connected cells according tothe ninth embodiment of the present invention, in order to storagecharge cells connected in series and maintain voltage balance betweenthe series-connected cells, first to Nth charging periods are set by acontrol circuit which is not illustrated in the figure.

Firstly, in a first half of the first charging period, the controlcircuit, not illustrated, turns on the switches Sa1 and Sb1. Then, aninput voltage Vin is input from the input terminal 101, and a chargingcurrent to charge the cell Cell1 with electric charge is stored in thecoil L1. A path of the charging current is indicated by a dotted arrowof FIG. 53.

Next, in a second half of the first charging period, the controlcircuit, not illustrated, turns off the switches Sa1 and Sb1 and turnson the switches Sf0 and Sf1. Then, the cell Cell1 is charged with thecharging current charged in the coil L1. A path of the charging currentis indicated by a dotted arrow of FIG. 54.

Next, in a first half of the second charging period, the controlcircuit, not illustrated, turns off the switches Sf0 and Sf1 and turnson the switches Sa2 and Sf0. Then, an input voltage Vin is input fromthe input terminal 101, and a charging current to charge the cell Cell2with electric charge is stored in the coil L1. A path of the chargingcurrent is indicated by a dotted arrow of FIG. 55. The path of thecharging current in FIG. 55 is in an opposite direction to the path ofthe charging current in FIG. 53.

Next, in a second half of the second charging period, the switches Sa2and Sf0 are turned off and the switches Sf1 and Sf2 are turned on. Then,the cell Cell2 is charged with the charging current charged in the coilL1. A path of the charging current is indicated by a dotted arrow ofFIG. 56.

After that, in a first half of the third charging period, the controlcircuit, not illustrated, turns off the switches Sf1 and Sf2 and turnson the switches Sf0 and Sf1. Then, an input voltage Vin is input fromthe input terminal 101, and a charging current to charge the cell Cell3with electric charge is stored in the coil L1. This state is the same asthe state in FIG. 53, and a path of the charging current is indicated bythe dotted arrow of FIG. 53.

Next, in a second half of the third charging period, the switches Sa1and Sb1 are turned off and the switches Sf2 and Sf3 are turned on. Then,the cell Cell3 is charged with the charging current stored in the coilL1. A path of the charging current is indicated by a dotted arrow ofFIG. 57.

Thereafter, a similar operation is repeated so as to alternately changea flowing direction of the charging current to be stored in the coil L1in a first half of each charging period, between an odd-numberedcharging period and an even-numbered charging period. Then,corresponding switches for both ends of each cell are turned on in asecond half of the each charging period, so as to charge the cell withthe charging current charged in the coil L1. Accordingly, in aneven-numbered charging period in which the cell CellN is charged, theswitches SfN−1 and SfN are turned on. A path of the charging current inthis state is indicated by a dotted arrow in FIG. 58.

Here, controlled contents by the control circuit, not illustrated, areexplained with reference to FIG. 59. FIG. 59 illustrates which switch,among the switches in FIG. 52, the control circuit, not illustrated,turns on in each of the first to Nth charging periods T1 to TN. That is,among the switches, a switch corresponding to a column indicative of“ON” in the figure is turned into an ON state by the control circuit,not illustrated, and the other switches are turned into an off state.

As illustrated in FIG. 59, the switches Sa1 and Sb1 are turned on in afirst half of an odd-numbered charging period, and the switches S21 andSf0 are turned on in a first half of an even-numbered charging period,so that the flowing direction of the charging current to be stored inthe coil L1 is changed alternately. Then, corresponding switches forboth ends of each cell are turned on in a second half of each of thecharging periods T1 to TN, as described above.

That is, a charging period of the control circuit, not illustrated,include: a charging period T1 including a period T1 a in which only theswitches Sa1 and Sb1 are turned on to charge the coil L1 with a chargingcurrent, and a period T1 b in which only the switches Sf0 and Sf1 areturned on to charge a first storage cell with the current of the coilthus charged; a charging period T2 similarly including a period T2 a inwhich only the switches Sa2 and Sf0 are turned on to charge the coil L1with a charging current, and a period T2 b in which only the switchesSf1 and Sf2 are turned on to charge a second storage cell with thecurrent of the coil L1 thus charged; and charging periods T3 to TN inwhich the switches Sa1, Sb1, Sa2, Sf0 and Sf2 to SfN are turned on andoff to charge third to Nth storage cells with the current of the coilL1, similarly to the charging periods T1 and T2. Voltages of therespective storage cells are monitored so as to control lengths of theperiods T1 a to TNa and lengths of the periods T1 b to TNb so that thevoltages of the respective storage cells are equal to each other.

Further, a discharge period of the control circuit, not illustrated,includes a period Tx having: a period Txa in which the voltages of therespective storage cells are monitored, a high-voltage storage cell of anumber P which is counted from a first storage cell and a low-voltagestorage cell of a number Q which is counted from the first storage cellare selected independently so that a sum of P and Q becomes an oddnumber, a switch SfP for connecting a high-voltage terminal of thehigh-voltage Pth storage cell to another end of the coil L and a switchSf(P−1) for connecting a low-voltage terminal of the high-voltage Pthstorage cell to one end of the coil L are turned on so as to charge thecoil L1 with a current; and a period Txb in which a switch SfQ forconnecting a high-voltage terminal of the low-voltage Qth storage cellto the another end of the coil L and a switch Sf(Q−1) for connecting alow-voltage terminal of the low-voltage Qth storage cell to the one endof the coil are turned on so as to charge the low-voltage storage cellwith the current of the coil. When driving a connected load to theoutput terminal 102, the control circuit, not illustrated, controlslengths of the above periods repeatedly so that the voltages of therespective storage cells are equal to each other.

As described, the control circuit, not illustrated, repeatedly controlseach of the switches to turn on as shown in the first to Nth chargingperiods T1 to TN described above. Accordingly, it is possible to realizea balance charging circuit for performing voltage boost and dropoperations by use of a single coil L1.

Further, each cell in the series-connected cells is not discharged inany of the charging periods T1 to TN, thereby also yielding an effectthat the series-connected cells which have a limitation in terms of thenumber of charging times can be charged with electric charge and voltagebalance between the series-connected cells can be maintained.

Moreover, the number of switches is equal to the number N of storagecells plus “4”, and therefore, it is possible to realize a balancecharging circuit for series-connected storage cells with an extremelyfew elements.

(Modification to Ninth Embodiment)

In the ninth embodiment, the control circuit, not illustrated, may bemodified to control the switches in the charging period T1 as follows.That is, FIGS. 60 to 62 are views illustrating on and off control statesof the switches Sa1, Sa2, Sb1, Sf0, Sf1, and Sf2 by the control circuitwhich is not illustrated in the ninth embodiment.

With reference to FIG. 60, the switches Sa1 and Sb1 are turned on in afirst half of the charging period T1 so as to store a current in thecoil L1. Then, in a second half of the charging period T1, the cellCell1 is charged with the current stored in the coil L1 by turning onthe switches Sf0 and Sf1.

Next, the switches Sa2 and Sf0 are turned on in a first half of thecharging period T2 so as to store a current in the coil L1. Then, in asecond half of the charging period T2, the cell Cell2 is charged withthe current stored in the coil L1 by turning on the switches Sf1 andSf2.

By turning on and off the switches as such, voltage boost and dropoperations of the balance charging circuit can be realized.

Further, with reference to FIG. 61, the switches Sa1 and Sf1 are turnedon in the first half of the charging period T1 so as to store a currentin the coil L1. Then, in the second half of the charging period T1, thecell Cell1 is charged with the current stored in the coil L1 by turningon the switches Sf0 and Sf1.

Next, the switches Sa2 and Sf0 are turned on in the first half of thecharging period T2 so as to store a current in the coil L1. Then, in thesecond half of the charging period T2, the cell Cell2 is charged withthe current stored in the coil L1 by turning on the switches Sf1 andSf2.

By turning on and off the switches as such, a voltage drop operation ofthe balance charging circuit can be realized.

Furthermore, with reference to FIG. 62, the switches Sa1 and Sb1 areturned on in the first half of the charging period T1 so as to store acurrent in the coil L1. Then, in the second half of the charging periodT1, the cell Cell1 is charged with the current stored in the coil L1 byturning on the switches Sa1 and Sf1.

Next, the switches Sa2 and Sf0 are turned on in the first half of thecharging period T2 so as to store a current in the coil L1. Then, in thesecond half of the charging period T2, the cell Cell2 is charged withthe current stored in the coil L1 by turning on the switches Sf1 andSf2.

By turning on and off the switches as such, a voltage boost operation ofthe balance charging circuit can be realized.

Note that such a control may be performed that an odd-numbered storagecell and an even-numbered storage cell are taken as a charging targetalternately, or such a control may be performed such that either ones ofodd-numbered storage cells and even-numbered storage cells are allcharged as a charging target completely at first in a random order,i.e., in any given order, and the other ones are then charged completelyas a charging target in a random order, i.e., in any given order. In acase where the former control is employed, a flowing direction of thecurrent is changed every time a storage cell to be a charging target ischanged, but in a case where the latter control is employed, the flowingdirection of the current is changed only once when the charging ischanged from the odd-numbered storage cells to the even-numbered storagecells and vice versa. Accordingly, in the case where the latter controlis employed, power consumption is more efficient than the case where theformer control is employed.

(Configuration of Balance Charging Circuit According to TenthEmbodiment)

FIG. 63 is a circuit diagram illustrating an exemplary configuration ofa balance charging circuit for charging, by use of a single coil L1, Npieces of storage cells Cell1 to CellN which are connected in series. InFIG. 63, the balance charging circuit includes a single coil L1, aswitch group SW1 for electrically connecting the coil L1 between aninput terminal 101 into which a charging voltage is input and areference voltage terminal, and a switch group SW2 for electricallyconnecting both ends of each of the storage cells Cell1 to CellN to bothends of the coil L1.

The switch group SW1 includes a switch Sa1, a switch Sa2, and a switchSb2. One ends of the switch Sa1 and the switch Sa2 are connected to theinput terminal 101, and another ends thereof are respectively connectedto one end and another end of the coil L1. One end of the switch Sb2 isconnected to the reference voltage terminal, and another end thereof isconnected to the other end of the coil L1.

The switch group SW2 includes switches Sc3 to ScN+1 and switches Sd2 toSdN. One ends of the switches Sc3 to ScN+1 are connected to contactpoints of N pieces of the storage cells Cell2 to CellN and an outputterminal 102, and another ends thereof are connected to the one end ofthe coil L1. One ends of the switches Sd2 to SdN are connected to thecontact points of N pieces of the storage cells Cell1 to CellN, andanother ends thereof are connected to the another end of the coil L1.

As described, the balance charging circuit according to the presentembodiment has such a configuration that the switch Sc2 is eliminatedfrom the balance charging circuit according to the eighth embodimentexplained with reference to FIG. 46.

(Operation of Balance Charging Circuit According to Tenth Embodiment)

Next, an operation of the balance charging circuit for series-connectedcells according to the tenth embodiment of the present invention will beexplained. FIGS. 64 to 69 are views to explain operations of the tenthembodiment of the present invention.

In the balance charging circuit for series-connected cells according tothe tenth embodiment of the present invention, in order to chargestorage cells connected in series and maintain voltage balance betweenthe series-connected cells, first to Nth charging periods are set by acontrol circuit which is not illustrated in the figure.

In a first half of the first charging period, the control circuit, notillustrated, turns on the switches Sa1 and Sd2. Then, an input voltageVin is input from the input terminal 101, so that the cell Cell1 ischarged while a charging current is stored in the coil L1. A path of thecharging current is indicated by a dotted arrow in FIG. 64.

Next, in a second half of the first charging period, the controlcircuit, not illustrated, turns off the switch Sa1 and turns on theswitch Sb2 while the switch Sd2 is being turned on. Then, the cell Cell1is charged with the charging current stored in the coil L1. A path ofthe charging current is indicated by a dotted arrow in FIG. 65.

Next, in a first half of the second charging period, the controlcircuit, not illustrated, turns off the switch Sd2 and turns on theswitches Sa2 and Sb2. Then, an input voltage Vin is input from the inputterminal 101, and a charging current to charge the cell Cell2 withelectric charge is stored in the coil L1. A path of the charging currentis indicated by a dotted arrow in FIG. 66.

Next, in a second half of the second charging period, the switches Sa2and Sb2 are turned off and the switches Sc3 and Sd2 are turned on. Then,the cell Cell2 is charged with the charging current stored in the coilL1. A path of the charging current is indicated by a dotted arrow inFIG. 67.

Thereafter, a similar operation is repeated to turn on the switches Sa2and Sb1 in a first half of each of the second charging period and itssubsequent charging periods, so as to store, in the coil L1, a chargingcurrent to charge a storage cell with electric charge. Then,corresponding switches for both ends of each cell are turned on in asecond half of the each charging period, so as to charge the cell withthe charging current stored in the coil L1. Accordingly, in a case wherethe cell CellN is charged, the switches ScN+1 and SdN are turned on. Apath of the charging current in this state is indicated by a dottedarrow in FIG. 68.

Here, controlled contents by the control circuit, not illustrated, areexplained with reference to FIG. 69. FIG. 69 illustrates which switch,among the switches in FIG. 63, the control circuit, not illustrated,turns on in each of the first to Nth charging periods T1 to TN. That is,among the switches, a switch corresponding to a column indicative of“ON” in the figure is turned into an ON state by the control circuit,not illustrated, and the other switches are turned into an off state.

As illustrated in FIG. 69, in each of the charging periods T1 to TN, theswitches Sa1 and Sd2 are turned on in the first half of the firstcharging period, and the switches Sa2 and Sb1 are turned on in a firsthalf of each of the second charging period and its subsequent chargingperiods. Then, corresponding switches for both ends of each cell areturned on in a second half of each of the charging periods T1 to TN, asdescribed above. As described, the control circuit, not illustrated,repeatedly controls each of the switches to turn on as shown in thefirst to Nth charging periods T1 to TN described above. Accordingly, itis possible to realize a balance charging circuit using a single coilL1.

Note that since a voltage drop operation is performed in the firstcharging period T1, the present embodiment is applicable to a case wherethe input voltage Vin is larger than a charging voltage of the cellCell1, and a direction of a charging current to the cell Cell1 may bedifferent from directions of charging currents to the cells Cell2 to N.

(Configuration of Balance Charging Circuit According to EleventhEmbodiment)

FIG. 70 is a circuit diagram illustrating an exemplary configuration ofa balance charging circuit for charging, by use of a single coil L1, Npieces of storage cells Cell1 to CellN which are connected in series. InFIG. 70, the balance charging circuit includes a single coil L1, aswitch group SW1 for electrically connecting an input terminal 101 intowhich a charging voltage is input and the coil L1, and a switch groupSW2 for electrically connecting both ends of each of the storage cellsCell1 to CellN to both ends of the coil L1.

The switch group SW1 includes a switch Sa1 and a switch Sb2. One end ofthe switch Sa1 is connected to the input terminal 101, and another endthereof is connected to one end of the coil L1. One end of the switchSb2 is connected to the reference voltage terminal, and another endthereof is connected to the one end of the coil L1.

The switch group SW2 includes switches Sc3 to ScN+1 and switches Sd2 toSdN. One ends of the switches Sc3 to ScN+1 are connected to contactpoints of N pieces of the storage cells Cell2 to CellN and an outputterminal 102, and another ends thereof are connected to the one end ofthe coil L1. One ends of the switches Sd2 to SdN are connected to thecontact points of N pieces of the storage cells Cell1 to CellN, andanother ends thereof are connected to another end of the coil L1.

As described, the balance charging circuit according to the presentembodiment has such a configuration that the switch Sc2 is eliminatedfrom the balance charging circuit according to the eighth embodimentexplained with reference to FIG. 46.

(Operation of Balance Charging Circuit According to Eleventh Embodiment)

Next, an operation of the balance charging circuit for series-connectedcells according to the eleventh embodiment of the present invention willbe explained. FIGS. 71 to 76 are views to explain operations of theeleventh embodiment of the present invention.

In the balance charging circuit for series-connected cells according tothe eleventh embodiment of the present invention, in order to chargeseries-connected storage cells and maintain voltage balance between theseries-connected cells, first to Nth charging periods are set by acontrol circuit which is not illustrated in the figure.

Ina first half of the first charging period, the control circuit, notillustrated, turns on the switches Sa1 and Sd2. Then, an input voltageVin is input from the input terminal 101, so that the cell Cell1 ischarged while a charging current is stored in the coil L1. A path of thecharging current is indicated by a dotted arrow in FIG. 71.

Next, in a second half of the first charging period, the controlcircuit, not illustrated, turns off the switch Sa1 and turns on theswitch Sb2 while the switch Sd2 is being turned on. Then, the cell Cell1is charged with the charging current charged in the coil L1. A path ofthe charging current is indicated by a dotted arrow in FIG. 72.

After that, in a first half of the second charging period, the controlcircuit, not illustrated, maintains the switches Sd2 and Sb2 to beturned on. This causes discharge from the cell Cell1, thereby storing,in the coil L1, a charging current to charge the cell Cell2 withelectric charge. A path of the charging current is indicated by a dottedarrow of FIG. 73.

Next, in a second half of the second charging period, the switch Sb2 isturned off and the switch Sc3 is turned on while the switch Sd2 is beingturned on. Then, the cell Cell2 is charged with the charging currentcharged in the coil L1. A path of the charging current is indicated by adotted arrow of FIG. 74.

Thereafter, a similar operation is repeated to turn on the switches Sb2and Sd2 in a first half of each of the second charging period and itssubsequent charging periods, so as to store, in the coil L1, a chargingcurrent to charge the other cells Cell2 to CellN with electric charge bydischarge from the cell Cell1. Accordingly, in a case where the cellCellN is charged, the switches ScN+1 and SdN are turned on. A path ofthe charging current in this state is indicated by a dotted arrow inFIG. 75.

Here, controlled contents by the control circuit, not illustrated, areexplained with reference to FIG. 76. FIG. 76 illustrates which switch,among the switches in FIG. 70, the control circuit, not illustrated,turns on in each of the first to Nth charging periods T1 to TN. That is,among the switches, a switch corresponding to a column indicative of“ON” in the figure is turned into an ON state by the control circuit,not illustrated, and the other switches are turned into an off state.

As illustrated in FIG. 76, in each of the charging periods T1 to TN, theswitches Sa1 and Sd2 are turned on in the first half of the firstcharging period so as to charge the cell Cell1, and the switches Sb2 andSd2 are turned on in a first half of each of the second charging periodand its subsequent charging periods so as to store, in the coil L1, acharging current to charge the other storage cells Cell2 to CellN withelectric charge by discharge from the cell Cell1. Then, correspondingswitches for both ends of each cell are turned on in a second half ofeach of the charging periods T1 to TN so as to charge the other cellsCell2 to CellN, as described above. As described, the control circuit,not illustrated, repeatedly controls each of the switches to turn on asshown in the first to Nth charging periods T1 to TN described above.Accordingly, it is possible to realize a balance charging circuit usinga single coil L1.

Note that since a voltage drop operation is performed in the firstcharging period T1, the present embodiment is applicable to a case wherethe input voltage Vin is larger than a charging voltage of the cellCell1, and discharge of the cell Cell1 is allowable.

(Configuration of Balance Charging Circuit According to TwelfthEmbodiment)

FIG. 77 is a circuit diagram illustrating an exemplary configuration ofa balance charging circuit for charging, by use of a single coil L1, Npieces of storage cells Cell1 to CellN which are connected in series. InFIG. 77, the balance charging circuit includes a single coil L1, aswitch group SW1 for electrically connecting an input terminal 101 intowhich a charging voltage is input and the coil L1, and a switch groupSW2 for electrically connecting both ends of each of the storage cellsCell1 to CellN to both ends of the coil L1.

The switch group SW1 includes a switch Sa1 and a switch Sb2. One end ofthe switch Sa1 is connected to the input terminal 101, and another endthereof is connected to one end of the coil L1. One end of the switchSb2 is connected to the reference voltage terminal, and another endthereof is connected to the one end of the coil L1.

The switch group SW2 includes switches Sc3 to ScN+1 and switches Sd2 toSdN. One ends of the switches Sc3 to ScN+1 are connected to contactpoints of N pieces of the storage cells Cell2 to CellN and an outputterminal 102, and another ends thereof are connected to the one end ofthe coil L1. One ends of the switches Sd2 to SdN are connected to thecontact points of N pieces of the storage cells Cell1 to CellN, andanother ends thereof are connected to another end of the coil L1.

As described, the balance charging circuit according to the presentembodiment has such a configuration that the switch Sc2 is eliminatedfrom the balance charging circuit according to the eighth embodimentexplained with reference to FIG. 46.

The configuration of the balance charging circuit in FIG. 77 itself issimilar to the configuration of the balance charging circuit explainedwith reference to FIG. 70, but some controlled contents of switchescontrolled by a control circuit, not illustrated, are different.

(Operation of Balance Charging Circuit According to Twelfth Embodiment)

Next, an operation of the balance charging circuit for series-connectedcells according to the twelfth embodiment of the present invention willbe explained. FIGS. 77 to 84 are views to explain operations of thetwelfth embodiment of the present invention.

In the balance charging circuit for series-connected cells according tothe twelfth embodiment of the present invention, in order to chargeseries-connected storage cells and maintain voltage balance between theseries-connected cells, first to Nth charging periods are set by acontrol circuit which is not illustrated in the figure.

In a first half of the first charging period, the control circuit, notillustrated, turns on the switches Sa1 and Sd2. Then, an input voltageVin is input from the input terminal 101, so that the cell Cell1 ischarged while a charging current is stored in the coil L1. A path of thecharging current is indicated by a dotted arrow of FIG. 78.

Next, in a second half of the first charging period, the controlcircuit, not illustrated, turns off the switch Sa1 and turns on theswitch Sb2 while the switch Sd2 is being turned on. Then, the cell Cell1is charged with the charging current stored in the coil L1. A path ofthe charging current is indicated by a dotted arrow of FIG. 79.

After that, in a first half of the second charging period, the controlcircuit, not illustrated, maintains the switches Sd2 and Sb2 to beturned on. This causes discharge from the cell Cell1, thereby storing,in the coil L1, a charging current to charge the cell Cell2 withelectric charge. A path of the charging current is indicated by a dottedarrow in FIG. 80.

Next, in a second half of the second charging period, the switch Sb2 isturned off and the switch Sc3 is turned on while the switch Sd2 is beingturned on. Then, the cell Cell2 is charged with the charging currentstored in the coil L1. A path of the charging current is indicated by adotted arrow of FIG. 81.

Then, in the third charging period and its subsequent periods, thecontrol circuit, not illustrated, turns on the switch Sb2 and theswitches Sd3 to SdN in a first half of each of the charging period tocause discharge from the cells Cell2 to CellN−1, thereby storing, in thecoil L1, a charging current to charge the cells Cell2 to CellN withelectric charge. Accordingly, in the charging period TN, the controlcircuit, not illustrated, turns on the switches Sb2 and SdN in the firsthalf of the charging period TN to cause discharge from the cellCell1N−1, thereby storing, in the coil L1, a charging current to chargethe cell CellN with electric charge. A path of the charging current isindicated by a dotted arrow of FIG. 82.

Next, in a second half of the charging period TN, the control circuit,not illustrated, turns on the switches SdN and ScN+1 to charge the cellCellN with the charging current stored in the coil L1. A path of thecharging current is indicated by a dotted arrow of FIG. 83.

Here, controlled contents by the control circuit, not illustrated, areexplained with reference to FIG. 84. FIG. 84 illustrates which switch,among the switches in FIG. 77, the control circuit, not illustrated,turns on in each of the first to Nth charging periods T1 to TN. That is,among the switches, a switch corresponding to a column indicative of“ON” in the figure is turned into an ON state by the control circuit,not illustrated, and the other switches are turned into an off state.

As illustrated in FIG. 84, in each of the charging periods T1 to TN, theswitches Sa1 and Sd2 are turned on in the first half of the firstcharging period so as to charge the cell Cell1, and the switch Sb2 and aswitch for sequentially causing the cells Cell1 to Cel1N−1 to dischargeare turned on in a first half of each of the second charging period andits subsequent charging periods so as to store a charging current in thecoil L1. Then, corresponding switches for both ends of each cell areturned on in a second half of each of the charging periods T1 to TN soas to charge the cells Cell2 to CellN, as described above. As described,the control circuit, not illustrated, repeatedly controls each of theswitches to turn on as shown in the first to Nth charging periods T1 toTN described above. Accordingly, it is possible to realize a balancecharging circuit using a single coil L1.

In the eleventh embodiment described above, the cell Cell1 is fixed as acell to be discharged, whereas the cell to be discharged is not fixedparticularly in the present exemplary embodiment, thereby making itpossible to reduce a burden to the cell Cell1.

Note that the present embodiment is applicable to a case where dischargeof the cell Cell1 to CellN−1 is allowable.

(Configuration of Balance Charging Circuit According to ThirteenthEmbodiment)

FIG. 85 is a circuit diagram illustrating an exemplary configuration ofa balance charging circuit for charging, by use of a single coil L1, Npieces of storage cells Cell1 to CellN which are connected in series. InFIG. 85, the balance charging circuit includes a single coil L1, aswitch group SW1 for electrically connecting an input terminal 101 intowhich a charging voltage is input and the coil L1, a switch group SW2for electrically connecting both ends of each of the storage cells Cell1to CellN to both ends of the coil L1, a diode D1, and a capacitor C1.

The switch group SW1 includes a switch Sa1 and a switch Sb2. One end ofthe switch Sa1 is connected to the input terminal 101, and another endthereof is connected to one end of the coil L1. One end of the switchSb2 is connected to a reference voltage terminal, and another endthereof is connected to the one end of the coil L1.

The switch group SW2 includes switches Sc3 to ScN+1 and switches Sd2 toSdN. One ends of the switches Sc3 to ScN+1 are connected to contactpoints of N pieces of the storage cells Cell2 to CellN and an outputterminal 102, and another ends thereof are connected to the one end ofthe coil L1. One ends of the switches Sd2 to SdN are connected to thecontact points of N pieces of the storage cells Cell1 to CellN, and theother ends thereof are connected to another end of the coil L1.

An anode of the diode D1 is connected to one end of the switch Sd2, anda cathode thereof is connected to a contact point between the storagecell Cell1 and the storage cell Cell2. This diode D1 is provided so asto suppress discharge from the storage cell Cell1.

The capacitor C1 is connected between the anode of the diode D1 and thereference voltage terminal. This capacitor C1 is provided to storeelectric charge once so as to store, in the coil L1, a current to chargethe storage cells Cell2 to CellN by discharge of the electric chargethus charged.

(Operation of Balance Charging Circuit According to ThirteenthEmbodiment)

Next, an operation of the balance charging circuit for series-connectedcells according to the thirteenth embodiment of the present inventionwill be explained. FIGS. 86 to 91 are views to explain operations of thethirteenth embodiment of the present invention.

In the balance charging circuit for series-connected cells according tothe thirteenth embodiment of the present invention, in order to chargeseries-connected storage cells and maintain voltage balance between theseries-connected cells, first to Nth charging periods are set by acontrol circuit which is not illustrated in the figure.

In a first half of the first charging period, the control circuit, notillustrated, turns on the switches Sa1 and Sd2. Then, an input voltageVin is input from the input terminal 101, so that the cell Cell1 ischarged while a charging current is stored in the coil L1. A path of thecharging current is indicated by a dotted arrow of FIG. 86. While thiscell Cell1 is charged, electric charge is stored in the capacitor C1.

Next, in a second half of the first charging period, the controlcircuit, not illustrated, turns off the switch Sa1 and turns on theswitch Sb2 while the switch Sd2 is being turned on. Then, the cell Cell1is charged with the charging current charged in the coil L1. A path ofthe charging current is indicated by a dotted arrow of FIG. 87.

After that, in a first half of the second charging period, the controlcircuit, not illustrated, maintains the switches Sd2 and Sb2 to beturned on. This causes discharge from the capacitor C1, thereby storing,in the coil L1, a charging current to charge the cell Cell2 withelectric charge. At this time, discharge from the cell Cell1 issuppressed by the diode D1. A path of the charging current is indicatedby a dotted arrow of FIG. 88.

Next, in a second half of the second charging period, the switch Sb2 isturned off and the switch Sc3 is turned on while the switch Sd2 is beingturned on. Then, the cell Cell2 is charged with the charging currentcharged in the coil L1. A path of the charging current is indicated by adotted arrow of FIG. 89.

Then, in the third charging period and its subsequent periods, thecontrol circuit, not illustrated, turns on the switch Sb2 and the switchSd2 in a first half of each charging period to cause discharge from thecapacitor C1, thereby storing, in the coil L1, a charging current tocharge the cells Cell3 to CellN with electric charge. Accordingly, inthe charging period TN, the control circuit, not illustrated, turns onthe switches Sb2 and Sd2 in a first half of the charging period TN tocause discharge from the capacitor C1, thereby storing, in the coil L1,a charging current to charge the cell CellN with electric charge. Thisstate is the same as the state in FIG. 88, and a path of the chargingcurrent is indicated by the dotted arrow of FIG. 88.

Next, in a second half of the charging period TN, the control circuit,not illustrated, turns on the switches SdN and ScN+1 to charge the cellCellN with the charging current stored in the coil L1. A path of thecharging current is indicated by a dotted arrow in FIG. 90.

Here, controlled contents by the control circuit, not illustrated, areexplained with reference to FIG. 91. FIG. 91 illustrates which switch,among the switches in FIG. 85, the control circuit, not illustrated,turns on in each of the first to Nth charging periods T1 to TN. That is,among the switches, a switch corresponding to a column indicative of“ON” in the figure is turned into an ON state by the control circuit,not illustrated, and the other switches are turned into an off state.

As illustrated in FIG. 91, in each of the charging periods T1 to TN, theswitches Sa1 and Sd2 are turned on in the first half of the firstcharging period so as to charge the cell Cell1 and store electric chargein the capacitor C1, and the switches Sb2 and Sd2 are turned on in afirst half of each of the second charging period and its subsequentcharging periods so as to store, in the coil L1, a charging current.Then, corresponding switches for both ends of each cell are turned on ina second half of each of the charging periods T1 to TN so as to chargethe cells Cell2 to CellN, as described above. As described, the controlcircuit, not illustrated, repeatedly controls each of the switches toturn on as shown in the first to Nth charging periods T1 to TN describedabove. Accordingly, it is possible to realize a balance charging circuitusing a single coil L1.

Note that the present embodiment is applicable to a case where it isnecessary that discharge of the cell Cell1 be suppressed.

(Configuration of Balance Charging Circuit According to FourteenthEmbodiment)

FIG. 92 is a circuit diagram illustrating an exemplary configuration ofa balance charging circuit for charging, by use of a single coil L1, Npieces of storage cells Cell1 to CellN which are connected in series. InFIG. 92, the balance charging circuit includes a single coil L1, aswitch group SW1 for electrically connecting an input terminal 101 intowhich a charging voltage is input and the coil L1, a switch group SW2for electrically connecting both ends of each of the storage cells Cell1to CellN to both ends of the coil L1, (N−1) pieces of diodes D1 to DN−1,and (N−1) pieces of capacitors C1 to CN−1.

The switch group SW1 includes a switch Sa1 and a switch Sb2. One end ofthe switch Sa1 is connected to the input terminal 101, and another endthereof is connected to one end of the coil L1. One end of the switchSb2 is connected to a reference voltage terminal, and another endthereof is connected to the one end of the coil L1.

The switch group SW2 includes switches Sc3 to ScN+1 and switches Sd2 toSdN. One ends of the switches Sc3 to ScN+1 are connected to contactpoints of N pieces of the storage cells Cell2 to CellN and an outputterminal 102, and another ends thereof are connected to the one end ofthe coil L1. One ends of the switches Sd2 to SdN are connected to thecontact points of N pieces of the storage cells Cell1 to CellN, andanother ends thereof are connected to another end of the coil L1.

The diodes D1 to DN−1 are provided so as to correspond to respectiveswitches Sd2 to SdN and respective storage cells Cell1 to CellN−1. Ananode of each of the diodes D1 to DN−1 is connected to one end of acorresponding one of the switches Sd2 to SdN, and a cathode thereof isconnected to a contact point between a corresponding storage cell andanother storage cell. These diodes D1 to DN−1 are each provided so as tosuppress discharge from a corresponding storage cell.

The capacitors C1 to CN−1 are each provided to store electric chargeonce so as to store, in the coil L1, a current to charge a correspondingone of the storage cells Cell2 to CellN by discharge of the electriccharge thus stored.

(Operation of Balance Charging Circuit According to FourteenthEmbodiment)

Next, an operation of the balance charging circuit for series-connectedcells according to the fourteenth embodiment of the present inventionwill be explained. FIGS. 93 to 99 are views to explain operations of thefourteenth embodiment of the present invention.

In the balance charging circuit for series-connected cells according tothe fourteenth embodiment of the present invention, in order to chargeseries-connected storage cells and maintain voltage balance between theseries-connected cells, first to Nth charging periods are set by acontrol circuit which is not illustrated in the figure.

Ina first half of the first charging period, the control circuit, notillustrated, turns on the switches Sa1 and Sd2. Then, an input voltageVin is input from the input terminal 101, so that the cell Cell1 ischarged while a charging current is stored in the coil L1. A path of thecharging current is indicated by a dotted arrow in FIG. 93. While thiscell Cell1 is charged, electric charge is stored in the capacitor C1.

Next, in a second half of the first charging period, the controlcircuit, not illustrated, turns off the switch Sa1 and turns on theswitch Sb2 while the switch Sd2 is being turned on. Then, the cell Cell1is charged with the charging current stored in the coil L1. A path ofthe charging current is indicated by a dotted arrow in FIG. 94.

After that, in a first half of the second charging period, the controlcircuit, not illustrated, maintains the switches Sd2 and Sb2 to beturned on. This causes discharge from the capacitor C1, thereby storing,in the coil L1, a charging current to charge the cell Cell2 withelectric charge. At this time, discharge from the cell Cell1 issuppressed by the diode D1. A path of the charging current is indicatedby a dotted arrow in FIG. 95.

Next, in a second half of the second charging period, the switch Sb2 isturned off and the switch Sc3 is turned on while the switch Sd2 is beingturned on. Then, the cell Cell2 is charged with the charging currentcharged in the coil L1. A path of the charging current is indicated by adotted arrow in FIG. 96.

Then, in the third charging period and its subsequent periods, thecontrol circuit, not illustrated, turns on the switch Sb2 and switchescorresponding to the capacitors C2 to CN−1 in a first half of each ofthe charging periods to cause discharge from the capacitor, therebystoring, in the coil L1, a charging current to charge the cells Cell3 toCellN with electric charge. Accordingly, in the charging period TN, thecontrol circuit, not illustrated, turns on the switches Sb2 and SdN in afirst half of the charging period TN to cause discharge from thecapacitor CN−1, thereby storing, in the coil L1, a charging current tocharge the cell CellN with electric charge. A path of the chargingcurrent is indicated by a dotted arrow in FIG. 97.

Next, in a second half of the charging period TN, the control circuit,not illustrated, turns on the switches SdN and ScN+1 to charge the cellCellN with the charging current charged in the coil L1. A path of thecharging current is indicated by a dotted arrow in FIG. 98.

Here, controlled contents by the control circuit, not illustrated, areexplained with reference to FIG. 99. FIG. 99 illustrates which switch,among the switches in FIG. 92, the control circuit, not illustrated,turns on in each of the first to Nth charging periods T1 to TN. That is,among the switches, a switch corresponding to a column indicative of“ON” in the figure is turned into an ON state by the control circuit,not illustrated, and the other switches are turned into an off state.

As illustrated in FIG. 99, in each of the charging periods T1 to TN, theswitches Sa1 and Sd2 are turned on in the first half of the firstcharging period so as to charge the cell Cell1 and store electric chargein the capacitor C1, and the switch Sb2 and switches corresponding toeach capacitor are turned on in a first half of each of the secondcharging period and its subsequent charging periods so as to store, inthe coil L1, a charging current. Then, corresponding switches for bothends of each cell are turned on in a second half of each of the chargingperiods T1 to TN so as to charge the cells Cell2 to CellN, as describedabove. As described, the control circuit, not illustrated, repeatedlycontrols each of the switches to turn on as shown in the first to Nthcharging periods T1 to TN described above. Accordingly, it is possibleto realize a balance charging circuit using a single coil L1.

Note that the present embodiment is applicable to a case where it isnecessary that discharge of the cells Cell1 to CellN be suppressed.

(Cell Balance Control 1 at the Time of Discharge)

As regard to the series-connected cells charged by the balance chargingcircuit for series-connected cells, at the time of discharge, that is,load driving, if a specific storage cell constituting theseries-connected cells is discharged in an unbalanced manner, the lifeof the cell may be shorten. Therefore, at the time of discharge of theseries-connected cells, it is preferable that the discharge is performedwhile charging voltages of respective storage cells constituting theseries-connected cells are kept in balance with each other.

In order to cause discharge while the charging voltages of the storagecells are kept in balance with each other, a storage cell having a highcharging voltage and a storage cell having a low charging voltage aresearched by current monitoring circuits, and the following operationsmay be performed.

For example, in the balance charging circuits explained with referenceto FIGS. 33, 39, and 46, a high-voltage storage cell CellP (P=1 to N)and a low-voltage storage cell CellQ (Q=1 to N, except for P) aresearched, and voltages of the respective storage cells are kept inbalance with each other by performing the following operations (1) and(2):

(1) The switch ScP+1 and the switch SdP are turned on in the chargingperiod Txa, so as to store a current in the coil L1 from the storagecell CellP; and

(2) The switch ScQ and the switch SdQ+1 are turned on in the chargingperiod Txb, so as to charge the storage cell CellQ with the currentstored in the coil L1 in the charging period Txa.

That is, as illustrated in FIG. 100, the switch SdP and the switch ScP+1are turned on by the control circuit, not illustrated, in the first halfperiod Txa of the charging period Tx. Further, the switch SdQ+1 and theswitch ScQ are turned on by the control circuit, not illustrated, in thesecond half period Txb of the charging period Tx.

(Cell Balance Control 2 at the Time of Discharge)

As regard to the balance charging circuits explained with reference toFIGS. 33, 39, and 46, a high-voltage storage cell CellP (P=1 to N) and alow-voltage storage cell CellQ (Q=1 to N, except for P) are searched,and the switches may be controlled as follows. For example, the switchScP and the switch SdP+1 are turned on by the control circuit, notillustrated, in the first half period Txa of the charging period Tx soas to store a current in the coil L1 from the storage cell CellP. Next,the switch ScQ+1 and the switch SdQ are turned on by the controlcircuit, not illustrated, in the second half period Txb of the chargingperiod Tx so as to charge the storage cell CellQ with the current thusstored in the coil L1.

That is, if Q>1 is satisfied, the switch ScP and the switch SdP+1 areturned on by the control circuit, not illustrated, in the first halfperiod Txa of the charging period Tx, as illustrated in FIG. 101.Further, the switch SdQ and the switch ScQ+1 are turned on by thecontrol circuit, not illustrated, in the second half period Txb of thecharging period Tx. However, if Q=1 is satisfied, the switch Sb1 and theswitch Sc2 are turned on by the control circuit, not illustrated, in thesecond half period Txb of the charging period Tx, as illustrated in FIG.102.

(Cell Balance Control 3 at the Time of Discharge)

In regard to the balance charging circuit explained with reference toFIG. 52, the cell balance at the time of discharge is limited tocharge-transfer from an odd-numbered storage cell to an even-numberedstorage cell and vice versa. A high-voltage storage cell CellP (P=1 toN) and a low-voltage storage cell CellQ (Q=1 to N, and P+Q is an oddnumber) are searched, and voltages of the respective storage cells arekept in balance with each other by performing the following operations(1) and (2):

(1) The switch SfP−1 and the switch SfP are turned on in the first halfperiod Txa of the charging period Tx, so as to store a current in thecoil L1 from the storage cell CellP; and

(2) The switch SfQ−1 and the switch SfQ are turned on in the second halfperiod Txb of the charging period Tx, so as to charge the storage cellCellQ with the current stored in the coil L1 in the period Txa.

That is, as illustrated in FIG. 103, the switch SfP−1 and the switch SfPare turned on by the control circuit, not illustrated, in the first halfperiod Txa of the charging period Tx. Further, the switch SfQ−1 and theswitch SfQ are turned on by the control circuit, not illustrated, in thesecond half period Txb of the charging period Tx.

(Cell Balance Control 4 at the Time of Discharge)

As regard to the balance charging circuit explained with reference toFIG. 63, a high-voltage storage cell CellP (P=1 to N) and a low-voltagestorage cell CellQ (Q=1 to N, except for P) are searched at the time ofdischarge, and the switches may be controlled as illustrated in FIGS.104 to 106.

That is, if P>1 is satisfied, the switch SdP and the switch ScP+1 areturned on by the control circuit, not illustrated, in the first halfperiod Txa of the charging period Tx, as illustrated in FIG. 104.Further, the switch ScQ and the switch SdQ+1 are turned on by thecontrol circuit, not illustrated, in the second half period Txb of thecharging period Tx.

However, if P=1 is satisfied, the switch Sb2 and the switch Sd2 areturned on by the control circuit, not illustrated, in the first halfperiod Txa of the charging period Tx, as illustrated in FIG. 105.Further, the switch ScQ and the switch SdQ+1 are turned on by thecontrol circuit, not illustrated, in the second half period Txb of thecharging period Tx.

Furthermore, if Q=1 is satisfied, the switch SdP and the switch ScP+1are turned on by the control circuit, not illustrated, in the first halfperiod Txa of the charging period Tx, as illustrated in FIG. 106.Further, the switch Sd2 and the switch Sb2 are turned on by the controlcircuit, not illustrated, in the second half period Txb of the chargingperiod Tx.

(Cell Balance Control 5 at the Time of Discharge)

As regard to the balance charging circuit explained with reference toFIG. 85, a high-voltage storage cell CellP (P=2 to N) and a low-voltagestorage cell CellQ (Q=1 to N, except for P) are searched at the time ofdischarge, and the switches may be controlled as illustrated in FIGS.107 and 108.

That is, if P>1 is satisfied, the switch SdP and the switch ScP+1 areturned on by the control circuit, not illustrated, in the first halfperiod Txa of the charging period Tx, as illustrated in FIG. 107.Further, the switch ScQ and the switch SdQ+1 are turned on by thecontrol circuit, not illustrated, in the second half period Txb of thecharging period Tx.

Furthermore, if Q=1 is satisfied, the switch SdP and the switch ScP+1are turned on by the control circuit, not illustrated, in the first halfperiod Txa of the charging period Tx, as illustrated in FIG. 108.Further, the switch Sd2 and the switch Sb2 are turned on by the controlcircuit, not illustrated, in the second half period Txb of the chargingperiod Tx.

In the balance charging circuit explained above with reference to FIG.85, the diode D1 is provided. Therefore, in a case of P=1, it isimpossible to perform cell balance at the time of discharge.

Note that as regard to the balance charging circuit explained withreference to FIG. 92, since the diodes D1 to DN−1 are provided, it isimpossible to perform cell balance at the time of discharge.

(Balance Charging Method for Series-Connected Storage Cells)

In the balance charging circuit for series-connected storage cellsaccording to each of the embodiments described above, the followingbalance charging method for series-connected storage cells isimplemented. That is, such a balance charging method forseries-connected storage cells is implemented in which a power issupplied from a power supply connected to an input terminal, and firstto Nth (N is an integer of 2 or more, the same applies hereinafter)storage cells connected in series sequentially from a reference voltageterminal between an output terminal and the reference voltage terminalare charged in a balanced manner, and which method includes: a firststep of electrically connecting a coil between the input terminal andthe reference voltage terminal and charging the coil with a chargingcurrent to charge the kth (1≦k≦N) storage cell; a second step ofelectrically connecting the coil to both ends of the kth storage celland charging the kth storage cell with the charging current charged inthe coil in the first step; and a third step of repeatedly performingthe first and second steps to charge the first to Nth storage cells oneby one. By employing this method, it is not necessary to provide aplurality of coils and it is possible to charge series-connected storagecells in a balanced manner by a single coil.

INDUSTRIAL APPLICABILITY

The balance charging circuit for series-connected cells according to thepresent invention is preferably applicable to a field such as anelectricity storage system.

REFERENCE SIGNS LIST

-   -   101, 201, 301, 401, 501: Input Terminal    -   102, 202, 302, 402, 502: Output Terminal    -   503: Charging Control Circuit    -   504: Cell Balancing Circuit    -   C1 to CN−1: Capacitor    -   Cell1 to CellN: Storage Cell    -   Control 1 to Control 6: Control Circuit    -   D1 to DN−1: Diode    -   L1, L2: Coil    -   M1, M2: Current Monitoring Circuit    -   S1 to S6: Switch

1. A balance charging circuit for series-connected storage cells forcharging, in a balanced manner, a first storage cell and a secondstorage cell connected in series and having one series-connected endconnected to an output terminal and another series-connected endconnected to a reference voltage terminal, the balancing chargingcircuit comprising: a coil provided in common for the first storage celland the second storage cell and temporarily storing a power suppliedfrom a power supply to charge the first storage cell and the secondstorage cell; and a switch section for electrically connecting the coilto one of the first storage cell and the second storage cell to chargethe one of the first storage cell and the second storage cell, and thenfor electrically connecting the coil to the other one of the firststorage cell and the second storage cell to charge the other one of thefirst storage cell and the second storage cell.
 2. The balance chargingcircuit for series-connected storage cells according to claim 1, whereinthe switch section includes a plurality of switches for switching a pathof a charging current flowing in the coil, the balance charging circuitfurther comprising: a control circuit for controlling the plurality ofswitches to be turned on and off and for setting repeatedly in turn afirst charging period in which the coil is charged with a chargingcurrent to charge the second storage cell, a second charging period inwhich the second storage cell is charged with the charging current thuscharged in the coil, a third charging period in which the coil ischarged with a charging current to charge the first storage cell, and afourth charging period in which the first storage cell is charged withthe charging current thus charged in the coil, wherein: in the firstcharging period, the control circuit controls the plurality of switchesto be turned on and off to form a path of a charging current flowinginto the reference voltage terminal through the coil; in the secondcharging period, the control circuit controls the plurality of switchesto be turned on and off to form a path of a charging current flowinginto the second storage cell from the coil; in the third chargingperiod, the control circuit controls the plurality of switches to beturned on and off to form a path of a charging current flowing into thereference voltage terminal through the coil; and in the fourth chargingperiod, the control circuit controls the plurality of switches to beturned on and off to electrically conduct one end of the coil to one endof the first storage cell, electrically conduct another end of the coilto another end of the first storage cell, and form a path of a chargingcurrent flowing into the first storage cell from the coil.
 3. Thebalance charging circuit for series-connected storage cells according toclaim 2, wherein the plurality of switches includes: a first switchhaving one end connected to a contact point where the first storage celland the second storage cell are connected to each other, a second switchhaving one end connected to an input terminal, a third switch having oneend connected to the reference voltage terminal, a fourth switch havingone end connected to the output terminal, a fifth switch having one endconnected to the reference voltage terminal, and a sixth switch havingone end connected to the contact point where the first storage cell andthe second storage cell are connected to each other, wherein one end ofthe coil is connected to another end of the first switch, another end ofthe second switch, and another end of the third switch, and another endof the coil is connected to another end of the fourth switch, anotherend of the fifth switch, and another end of the sixth switch, andwherein in the first charging period, the control circuit turns on thesecond and sixth switches and turns off the first, third, fourth, andfifth switches, in the second charging period, the control circuit turnson the third and sixth switches and turns off the first, second, fourth,and fifth switches, in the third charging period, the control circuitturns on the second and fifth switches and turns off the first, third,fourth, and sixth switches, and in the fourth charging period, thecontrol circuit turns on the first and fourth switches and turns off thesecond, third, fifth, and sixth switches.
 4. The balance chargingcircuit for series-connected storage cells according to claim 2, whereinthe plurality of switches includes: a first switch having one endconnected to a contact point where the first storage cell and the secondstorage cell are connected to each other, a second switch having one endconnected to an input terminal, a third switch having one end connectedto the reference voltage terminal, a fourth switch having one endconnected to the output terminal, a fifth switch having one endconnected to the reference voltage terminal, and a sixth switch havingone end connected to the contact point where the first storage cell andthe second storage cell are connected to each other, wherein one end ofthe coil is connected to another end of the first switch, another end ofthe second switch, and another end of the third switch, and another endof the coil is connected to another end of the fourth switch, anotherend of the fifth switch, and another end of the sixth switch, andwherein in the first charging period, the control circuit turns on thesecond and fifth switches and turns off the first, third, fourth, andsixth switches, in the second charging period, the control circuit turnson the third and sixth switches and turns off the first, second, fourth,and fifth switches, in the third charging period, the control circuitturns on the second and fifth switches and turns off the first, third,fourth, and sixth switches, and in the fourth charging period, thecontrol circuit turns on the first and fourth switches and turns off thesecond, third, fifth, and sixth switches.
 5. The balance chargingcircuit for series-connected storage cells according to claim 2, whereinthe plurality of switches includes: a first switch having one endconnected to the output terminal, a second switch having one endconnected to an input terminal, a third switch having one end connectedto the reference voltage terminal, a fourth switch having one endconnected to the input terminal, and a fifth switch having one endconnected to a contact point where the first storage cell and the secondstorage cell are connected to each other, wherein one end of the coil isconnected to another end of the first switch, another end of the secondswitch, and another end of the third switch, and another end of the coilis connected to another end of the fourth switch and another end of thefifth switch, and wherein in the first charging period, the controlcircuit turns on the second and fifth switches and turns off the first,third, and fourth switches, in the second charging period, the controlcircuit turns on the third and fifth switches and turns off the first,second, and fourth switches, in the third charging period, the controlcircuit turns on the third and fourth switches and turns off the first,second, and fifth switches, and in the fourth charging period, thecontrol circuit turns on the first and fifth switches and turns off thesecond, third, and fourth switches.
 6. The balance charging circuit forseries-connected storage cells according to claim 2, wherein theplurality of switches includes: a first switch having one end connectedto the output terminal, a second switch having one end connected to aninput terminal, and a third switch having one end connected to thereference voltage terminal, wherein one end of the coil is connected toanother end of the first switch, another end of the second switch, andanother end of the third switch, and another end of the coil isconnected to a contact point where the first storage cell and the secondstorage cell are connected to each other, and wherein in the firstcharging period, the control circuit turns on the second switch andturns off the first and third switches, in the second charging period,the control circuit turns on the third switch and turns off the firstand second switches, in the third charging period, the control circuitturns on the third switch and turns off the first and second switches,and in the fourth charging period, the control circuit turns on thefirst switch and turns off the second and third switches.
 7. The balancecharging circuit for series-connected storage cells according to claim2, wherein the plurality of switches includes: a first switch having oneend connected to the output terminal, a second switch having one endconnected to an input terminal, and a third switch having one endconnected to the reference voltage terminal, the balance chargingcircuit further comprising: a capacitor having one end connected to thereference voltage terminal, and a diode having a cathode connected to acontact point where the first storage cell and the second storage cellare connected to each other, wherein one end of the coil is connected toanother end of the first switch, another end of the second switch, andanother end of the third switch, and another end of the coil isconnected to another end of the capacitor and an anode of the diode, andwherein in the first charging period, the control circuit turns on thesecond switch and turns off the first and third switches, in the secondcharging period, the control circuit turns on the third switch and turnsoff the first and second switches, in the third charging period, thecontrol circuit turns on the third switch and turns off the first andsecond switches, and in the fourth charging period, the control circuitturns on the first switch and turns off the second and third switches.8. The balance charging circuit for series-connected storage cellsaccording to claim 5, wherein the control circuit sets times for turningon the switches in the second and fourth charging periods so that thecharging current of the coil becomes zero at the end of the second andfourth charging periods.
 9. A balance charging circuit forseries-connected storage cells in which a power is supplied from a powersupply connected to an input terminal, and first to Nth (N is an integerof 2 or more, the same applies hereinafter) storage cells connected inseries sequentially from a reference voltage terminal between an outputterminal and the reference voltage terminal are charged in a balancedmanner, the balance charging circuit comprising: a coil for storing apower supplied from the power supply and charging the first to Nthstorage cells; a first switch group for electrically connecting the coilbetween the input terminal and the reference voltage terminal; and asecond switch group for electrically connecting the coil to both ends ofeach of the first to Nth storage cells to charge the each of the firstto Nth storage cells, wherein the first to Nth storage cells are chargedone by one.
 10. The balance charging circuit for series-connectedstorage cells according to claim 9, further comprising: a controlcircuit for repeatedly setting each of first to Nth charging periodswherein a kth (1≦k≦N) coil charging period in which the first switchgroup is controlled to be turned on and off to charge the coil with acharging current to charge the kth storage cell, and a kth storage cellcharging period in which the second switch group is controlled to beturned on and off to charge the kth storage cell with the chargingcurrent charged in the coil in the kth coil charging period are taken asa kth charging period for charging the kth storage cell, wherein: in thekth coil charging period, the control circuit controls the first switchgroup to be turned on and off to form a path of a charging currentflowing into the reference voltage terminal through the coil, and in thekth storage cell charging period, the control circuit controls thesecond switch group to be turned on and off to form a path of a chargingcurrent flowing into the kth storage cell from the coil.
 11. The balancecharging circuit for series-connected storage cells according to claim10, wherein the first switch group includes: a first coil connectionswitch having one end connected to the input terminal and another endconnected to one end of the coil, and a second coil connection switchhaving one end connected to another end of the coil and another endconnected to the reference voltage terminal; and wherein the secondswitch group includes: first to Nth storage cell lower side connectionswitches each having one end connected to a lower side of each of thefirst to Nth storage cells, and another end connected to the one end ofthe coil, and first to (N−1)th storage cell upper side connectionswitches each having one end connected to an upper side of each of thefirst to (N−1)th storage cells, and another end connected to the anotherend of the coil.
 12. The balance charging circuit for series-connectedstorage cells according to claim 11, wherein in the kth coil chargingperiod, the control circuit turns on the first and second coilconnection switches, and turns off the first to Nth storage cell lowerside connection switches and the first to (N−1)th storage cell upperside connection switches; and in the kth storage cell charging period,the control circuit turns off the first and second coil connectionswitches, turns on the kth storage cell lower side connection switch andthe kth storage cell upper side connection switch, and turns off theswitches other than the kth storage cell lower side connection switchamong the second to Nth storage cell lower side connection switches, andthe switches other than the kth storage cell upper side connectionswitch among the first to (N−1)th storage cell upper side connectionswitches.
 13. The balance charging circuit for series-connected storagecells according to claim 11, wherein in the first coil charging period,the control circuit turns on the first coil connection switch and thefirst storage cell upper side connection switch, and turns off thesecond coil connection switch, the first to Nth storage cell lower sideconnection switches, and the second to (N−1)th storage cell upper sideconnection switches; in the Mth (2≦M≦N) coil charging period, thecontrol circuit turns on the first and second coil connection switches,and turns off the first to Nth storage cell lower side connectionswitches and the first to (N−1)th storage cell upper side connectionswitches, in the first storage cell charging period, the control circuitturns off the first and second coil connection switches, turns on thefirst storage cell lower side connection switch and the first storagecell upper side connection switch, and turns off the switches other thanthe first storage cell lower side connection switch among the first toNth storage cell lower side connection switches, and the switches otherthan the first storage cell upper side connection switch among the firstto (N−1)th storage cell upper side connection switches, and in the Mthstorage cell charging period, the control circuit turns off the firstand second coil connection switches, turns on the Mth storage cell lowerside connection switch and the Mth storage cell upper side connectionswitch, and turns off the switches other than the Mth storage cell lowerside connection switch among the first to Nth storage cell lower sideconnection switches, and the switches other than the Mth storage cellupper side connection switch among the first to (N−1)th storage cellupper side connection switches.
 14. The balance charging circuit forseries-connected storage cells according to claim 11, wherein in thefirst storage cell charging period, the control circuit turns on thefirst and second coil connection switches, and turns off the first toNth storage cell lower side connection switches and the first to (N−1)thstorage cell upper side connection switches, in the Mth coil chargingperiod, the control circuit turns on the first and second coilconnection switches, and turns off the first to Nth storage cell lowerside connection switches and the first to (N−1)th storage cell upperside connection switches, in the first storage cell charging period, thecontrol circuit turns on the first coil connection switch and the firststorage cell upper side connection switch, and turns off the second coilconnection switch, the first to Nth storage cell lower side connectionswitches, and the switches other than the first storage cell upper sideconnection switch among the first to (N−1)th storage cell upper sideconnection switches, and in the Mth storage cell charging period, thecontrol circuit turns off the first and second coil connection switches,turns on the Mth storage cell lower side connection switch and the Mthstorage cell upper side connection switch, and turns off the switchesother than the Mth storage cell lower side connection switch among thefirst to Nth storage cell lower side connection switches, and theswitches other than the Mth storage cell upper side connection switchamong the first to (N−1)th storage cell upper side connection switches.15. The balance charging circuit for series-connected storage cellsaccording to claim 10, wherein the first switch group includes: a firstcoil connection switch having one end connected to the input terminaland another end connected to one end of the coil, a second coilconnection switch having one end connected to another end of the coiland another end connected to the reference voltage terminal, a thirdcoil connection switch having one end connected to the input terminaland another end connected to the another end of the coil, and a fourthcoil connection switch having one end connected to the one end of thecoil and another end connected to the reference voltage terminal, andwherein the second switch group includes: a kth (k is an even number)storage cell connection switch having one end connected to a lower sideof each of the first to Nth storage cells and the output terminal, andanother end connected to the one end of the coil, and a kth (k is an oddnumber) storage cell connection switch having one end connected to anupper side of each of the first to (N−1)th storage cells, and anotherend connected to the another end of the coil.
 16. The balance chargingcircuit for series-connected storage cells according to claim 15,wherein in the kth (k is an odd number) coil charging period, thecontrol circuit turns on the first and second coil connection switches,and turns off the third and fourth coil connection switches and thefirst to Nth storage cell connection switches, in the kth (k is an evennumber) coil charging period, the control circuit turns on the third andfourth coil connection switches, and turns off the first and second coilconnection switches and the first to Nth storage cell connectionswitches, in the first storage cell charging period, the control circuitturns on the fourth coil connection switch and the first storage cellconnection switch, and turns off the first to third coil connectionswitches and the second to Nth storage cell connection switches, and inthe kth (k≧2) storage cell charging period, the control circuit turns onthe kth storage cell connection switch and the (k−1)th storage cellconnection switch, and turns off the first to fourth coil connectionswitches and the switches other than the kth and (k−1)th storage cellconnection switches among the first to Nth storage cell connectionswitches.
 17. The balance charging circuit for series-connected storagecells according to claim 16, wherein in the first coil charging period,the control circuit turns on the first storage cell connection switchinstead of turning on the second coil connection switch.
 18. The balancecharging circuit for series-connected storage cells according to claim16, wherein in the first storage cell charging period, the controlcircuit turns on the first coil connection switch instead of turning onthe fourth coil connection switch.
 19. The balance charging circuit forseries-connected storage cells according to claim 10, wherein the firstswitch group includes: a first coil connection switch having one endconnected to the input terminal and another end connected to one end ofthe coil, a second coil connection switch having one end connected tothe input terminal and another end connected to another end of the coil,and a third coil connection switch having one end connected to the oneend of the coil and another end connected to the reference voltageterminal, and wherein the second switch group includes: first to (N−1)thstorage cell lower side connection switches each having one endconnected to a lower side of each of the third to Nth storage cells andthe output terminal, and another end connected to the one end of thecoil, and first to (N−1)th storage cell upper side connection switcheseach having one end connected to an upper side of each of the first to(N−1)th storage cells, and another end connected to the another end ofthe coil.
 20. The balance charging circuit for series-connected storagecells according to claim 19, wherein in the first coil charging period,the control circuit turns on the first coil connection switch and thefirst storage cell upper side connection switch, in the second to Nthcoil charging periods, the control circuit turns on the second and thirdcoil connection switches, and turns off the first to (N−1)th storagecell lower side connection switches and the first to (N−1)th storagecell upper side connection switches, in the first storage cell chargingperiod, the control circuit turns on the third coil connection switchand the first storage cell upper side connection switch, and turns offthe first to (N−1)th storage cell lower side connection switches, andthe switches other than the first storage cell upper side connectionswitch among the first to (N−1)th storage cell upper side connectionswitches, and in the kth (k≧2) storage cell charging period, the controlcircuit turns off the first to third coil connection switches, turns onthe (k+1)th storage cell lower side connection switch and the kthstorage cell upper side connection switch, and turns off the switchesother than the (k+1)th storage cell lower side connection switch amongthe first to (N−1)th storage cell lower side connection switches, andthe switches other than the kth storage cell upper side connectionswitch among the first to (N−1)th storage cell upper side connectionswitches.
 21. The balance charging circuit for series-connected storagecells according to claim 10, wherein the first switch group includes: afirst coil connection switch having one end connected to the inputterminal and another end connected to one end of the coil, and a secondcoil connection switch having one end connected to the one end of thecoil and another end connected to the reference voltage terminal, andwherein the second switch group includes: first to (N−1)th storage celllower side connection switches each having one end connected to a lowerside of each of the third to Nth storage cells and the output terminal,and another end connected to the one end of the coil, and first to(N−1)th storage cell upper side connection switches each having one endconnected to an upper side of each of the first to (N−1)th storagecells, and another end connected to another end of the coil.
 22. Thebalance charging circuit for series-connected storage cells according toclaim 21, wherein in the first coil charging period, the control circuitturns on the first coil connection switch and the first storage cellupper side connection switch, in the second to Nth coil chargingperiods, the control circuit turns on the second coil connection switchand the first storage cell upper side connection switch, and turns offthe first to (N−1)th storage cell lower side connection switches and thesecond to (N−1)th storage cell upper side connection switches, in thefirst storage cell charging period, the control circuit turns on thesecond coil connection switch and the first storage cell upper sideconnection switch, and turns off the first to (N−1)th storage cell lowerside connection switches and the second to (N−1)th storage cell upperside connection switches, and in the kth (k≧2) storage cell chargingperiod, the control circuit turns off the first and second coilconnection switches, turns on the (k+1)th storage cell lower sideconnection switch and the kth storage cell upper side connection switch,and turns off the switches other than the (k+1)th storage cell lowerside connection switch among the first to (N−1)th storage cell lowerside connection switches, and the switches other than the kth storagecell upper side connection switch among the first to (N−1) storage cellupper side connection switches.
 23. The balance charging circuit forseries-connected storage cells according to claim 22, wherein in the kth(2≦k≦N) coil charging period, the control circuit turns on the secondcoil connection switch and the (k−1)th storage cell upper sideconnection switch, and turns off the first to (N−1)th storage cell lowerside connection switches, and the switches other than the (k−1)thstorage cell upper side connection switch among the first to (N−1)thstorage cell upper side connection switches.
 24. The balance chargingcircuit for series-connected storage cells according to claim 10,wherein the first switch group includes: a first coil connection switchhaving one end connected to the input terminal and another end connectedto one end of the coil, and a second coil connection switch having oneend connected to the one end of the coil and another end connected tothe reference voltage terminal, and wherein the second switch groupincludes: first to (N−1)th storage cell lower side connection switcheseach having one end connected to a lower side of each of the third toNth storage cells and the output terminal, and another end connected tothe one end of the coil, and first to (N−1)th storage cell upper sideconnection switches each having one end connected to an upper side ofeach of the first to (N−1)th storage cells, and another end connected toanother end of the coil, and wherein the balance charging circuitfurther comprising: a diode having a cathode connected to the upper sideof the first storage cell and an anode connected to the first storagecell upper side connection switch; and a capacitor connected between theanode of the diode and the reference voltage terminal.
 25. The balancecharging circuit for series-connected storage cells according to claim10, wherein the first switch group includes: a first coil connectionswitch having one end connected to the input terminal and another endconnected to one end of the coil, a second coil connection switch havingone end connected to the one end of the coil and another end connectedto the reference voltage terminal, and the second switch groupcomprising: first to (N−1)th storage cell lower side connection switcheseach having one end connected to a lower side of each of the third toNth storage cells and the output terminal, and another end connected tothe one end of the coil, and first to (N−1)th storage cell upper sideconnection switches each having one end connected to an upper side ofeach of the first to (N−1)th storage cells, and another end connected toanother end of the coil, the balance charging circuit furthercomprising: first to (N−1)th diodes each provided for each of the firstto (N−1)th storage cells and having a cathode connected to an upper sideof a corresponding storage cell and an anode connected to each of thefirst to (N−1)th storage cell upper side connection switches; a firstcapacitor connected between an anode of the first diode and thereference voltage terminal; and second to (N−1)th capacitors eachprovided for each of the second to (N−1)th diodes and connected betweenan anode of a corresponding diode and an anode of a diode provided at alower side of the corresponding diode.
 26. The balance charging circuitfor series-connected storage cells according to claim 24, wherein in thefirst coil charging period, the control circuit turns on the first coilconnection switch and the first storage cell upper side connectionswitch; in the second to Nth coil charging periods, the control circuitturns on the second coil connection switch and the first storage cellupper side connection switch, and turns off the first to (N−1)th storagecell lower side connection switches and the second to (N−1)th storagecell upper side connection switches; in the first storage cell chargingperiod, the control circuit turns on the second coil connection switchand the first storage cell upper side connection switch, and turns offthe first to (N−1)th storage cell lower side connection switches and thesecond to (N−1)th storage cell upper side connection switches; and inthe kth (k≧2) storage cell charging period, the control circuit turnsoff the first and second coil connection switches, turns on the (k−1)thstorage cell lower side connection switch and the (k−1)th storage cellupper side connection switch, and turns off the switches other than the(k−1)th storage cell lower side connection switch among the first to Nthstorage cell lower side connection switches, and the switches other thanthe (k−1)th storage cell upper side connection switch among the first to(N−1) storage cell upper side connection switches.
 27. The balancecharging circuit for series-connected storage cells according to claim10, wherein the first switch group includes: a first coil connectionswitch having one end connected to the input terminal and another endconnected to one end of the coil, and a second coil connection switchhaving one end connected to another end of the coil and another endconnected to the reference voltage terminal; and wherein the secondswitch group includes: first to Nth storage cell lower side connectionswitches each having one end connected to a lower side of each of thefirst to Nth storage cells, and another end connected to the one end ofthe coil, and first to Nth storage cell upper side connection switcheseach having one end connected to an upper side of each of the first toNth storage cells, and another end connected to the another end of thecoil.
 28. The balance charging circuit for series-connected storagecells according to claim 27, wherein in the first to Nth coil chargingperiods, the control circuit turns on the first coil connection switchand the second coil connection switch, and turns off the first to Nthstorage cell lower side connection switches and the first to Nth storagecell upper side connection switches; and in the kth (1≦k≦N) storage cellcharging period, the control circuit turns on the kth storage cell lowerside connection switch and the kth storage cell upper side connectionswitch, and turns off the switches other than the kth storage cell lowerside connection switch among the first to Nth storage cell lower sideconnection switches, and the switches other than the kth storage cellupper side connection switch among the first to Nth storage cell upperside connection switches.
 29. The balance charging circuit forseries-connected storage cells according to claim 16, wherein after alloperations corresponding to the kth (k is an odd number) coil chargingperiod and the kth (k is an odd number) storage cell charging period arecompleted, the control circuit controls the first and second switchgroups to be turned on and off so that operations corresponding to thekth (k is an even number) coil charging period and the kth (k is an evennumber) storage cell charging period are performed.
 30. The balancecharging circuit for series-connected storage cells according to claim16, wherein after all operations corresponding to the kth (k is an evennumber) coil charging period and the kth (k is an even number) storagecell charging period are completed, the control circuit controls thefirst and second switch groups to be turned on and off so thatoperations corresponding to the kth (k is an odd number) coil chargingperiod and the kth (k is an odd number) storage cell charging period areperformed.
 31. The balance charging circuit for series-connected storagecells according to claim 9, wherein the control circuit controls thefirst and second switch groups so that the Pth (P is any of 1 to N)storage cell having a higher voltage among the first to Nth storagecells is electrically connected to both ends of the coil to store acurrent in the coil from the Pth storage cell, and after that, the Qth(Q is any of 1 to N except P) storage cell having a lower voltage iselectrically connected to the both ends of the coil to store, in the Qthstorage cell, the current thus stored in the coil, thereby maintainingcharging voltage balance between the Pth storage cell and the Qthstorage cell.
 32. A balance charging method for series-connected storagecells in which a power is supplied from a power supply connected to aninput terminal, and first to Nth (N is an integer of 2 or more, the sameapplies hereinafter) storage cells connected in series sequentially froma reference voltage terminal between an output terminal and thereference voltage terminal are charged in a balanced manner, the balancecharging method comprising: a first step of electrically connecting acoil between the input terminal and the reference voltage terminal andcharging the coil with a charging current to charge the kth (1≦k≦N)storage cell; a second step of electrically connecting the coil to bothends of the kth storage cell and charging the kth storage cell with thecharging current charged in the coil in the first step; and a third stepof repeatedly performing the first and second steps to charge the firstto Nth storage cells one by one.